New Trends in Ophthalmology: Medical and Surgical Management Samuel Boyd, Benjamin F Boyd
INDEX
×
Chapter Notes

Save Clear


Evaluation and Treatment of Ocular Surface DiseasesChapter 1

Alejandro Navas, MD, MSc
Julio C. Hernandez-Camarena, MD
Enrique O. Graue-Hernandez, MD
 
Introduction
 
Ocular Surface Homeostasis
The ocular surface is composed by conjunctiva (covering the inner lid surfaces and the globe), corneoscleral limbus, corneal epithelium and tear film. These components are dependent of the correct function of the ocular adnexa including the anterior lamella of the lids, the eyelashes and the lacrimal system in order to obtain normal function. The final goal of the ocular surface elements and their adjacent aid structures is to maintain the optic clarity of the cornea, either by regulating the hydration of the cornea and conjunctiva or by protecting them from trauma, infections, toxic stimuli or mechanical damage.(1)
The first defense mechanisms of the ocular surface are the eyelids. They protect from trauma and from dehydration, hence if any anatomical or functional abnormality of the lid is found, the first line of therapy in alleviating any ocular disease is to attempt to correct the normal eyelid physiology.(1) The eyelid skin is specialized; it is the thinnest skin on the body allowing for minimal resistance during eyelid opening and it also lacks of hair follicles in the pretarsal, preseptal and orbicularis skin; it has 100 upper eyelid cilia (lashes) and 50 in the inferior lid. These last help catching small debris and prevent them from depositing on the ocular surface.(2) The margin eyelid also contains meibomian glands that produce and secrete lipids to the tear film. These lipids are essential for the optimal function of the tear film, since they act as surfactant by uniformly distributing the tear and by delaying its evaporation. Chronic inflammation of the meibomian glands (i.e. infectious blepharitis, rosacea, cicatricial pemphigoid) can lead to tear film dysfunction, chronic evaporative dry eye and even to abnormalities of the eyelashes (distichiasis), contributing to a chronicity.(3)
Dysfunction of the lid musculature can lead to ocular surface pathology. The orbicularis muscle is innervated by the seventh cranial nerve and is responsible for blinking, for keeping a proper lid closure during sleep, and contributes to normal eyelid tension and pumping of tears to the lacrimal drainage system. The pretarsal portion is responsible for unconscious blinking while the other two portions (preseptal and orbicular) are responsible for voluntary blinking.(2,4) Any pathology affecting the seventh cranial nerve (either central or peripheral) or the muscle itself (myastenia gravis, trauma or inflammatory) can result in chronic ocular surface exposure secondary to lagophthalmos, lower lid ectropion, decreased or incomplete blinking.(1)
Malfunction of the eyelid retractors (i.e. levator palpebrae muscle and Müller's muscle) generally result from neurogenic, myogenic, aponeurotic, mechanical and traumatic mechanisms and manifest as ptosis and dermatochalasis. These last are common in aging population, and their surgical overcorrection often ends up in iatrogenic lagophthalmos, exposure keratopathy and chronic ocular surface disease.(5) Desinsertion of the inferior eyelid retractors commonly induce lower lid entropion, requiring surgical correction to avoid exposure keratopathy from mechanical trauma (inverted eyelashes and keratinized skin).(6)
The conjunctiva is an essential component of the ocular surface homeostasis. It is a mucous layer derived from the surface ectoderm that lines the globe from the mucocutaneous junction of the eyelid margin to the corneoscleral limbus. The histological structure of the conjunctiva is that from a stratified columnar non keratinized epithelium. It is largely populated by goblet cells (5-10% of the cells) that produce mucin, a carbohydrate rich substance essential in the tear film homeostasis.(7) The conjunctiva has a basal membrane (collagen type IV) and a substantia propria rich in immune elements (lymphocytes, mast cells, antigen 2presenter cells, i.e. Langherhans cells) which enables it to respond quickly against infections and trauma, but also very sensitive to allergic pathology.(7) It has a rapid healing rate, which is attributed to the presence of conjunctival epithelial stem cells and proliferating goblet cells, which are preferably located in the fornix.(8) The conjunctiva responds to injury, low-grade inflammation or nutritional deficiency by increasing the mucin production. However, chronic inflammation of the conjunctiva as seen in immune mediated diseases (cicatricial pemphigoid, Steven-Johnsons) induces squamous metaplasia, resulting in keratinization of the epithelium and loss of goblet cells.(1) This endures a vicious cycle where the continuous mechanical injury and unstable tear film provide additional stimuli for inflammation and anatomical distortion. If the inflammatory stimuli are not tampered, conjunctival scarring will occur, resulting in fornix foreshortening, symblepharon, motility restriction, lagophthalmos and chronic exposure, which may end up in severe keratinization.(1)
The tear film importance will be discussed later, but in general, it is essential in creating a uniform refractive surface, to lubricate and minimize the mechanical trauma of the eyelids, it is essential as defense mechanism against microorganism's invasion and it provides trophic and oxygen support to the ocular surface cells.
By all the means, the ocular surface has evolved to protect and nourish a highly specialized tissue, the cornea. The cornea is the main optical component of the eye, it must maintain transparency to visible light and resist external injuries as trauma, microbial invasion and dehydration. It is composed of 5 specialized layers, being the two first outer layers (epithelium and Bowman's layer) responsible for immediate protection from external grievance.(9) The epithelium is non keratinized stratified squamous, and as in skin, the basal cells have continuous mitotic activity and originate daughter cells that differentiate as they migrate toward the surface.(9) All epithelial cells have gap junctions and complex systems of desmosomes that confer a degree of protection to external noxious agents.(10) The surface corneal epithelium, as does the conjunctival epithelium, has external microvilli that secrete mucin and other glycoprotein to form the glycocalyx. The latter allows an even distribution of the tear film and increases the area of oxygen distribution in the avascular cornea.(11)
Finally, the corneoscleral limbus is the anatomical transition from esclera to cornea where conjuctival columnar epithelium shifts to the stratified squamous epithelium of the cornea.(9) The vascular plexus of the substantia propria on the conjunctiva also ends up here in a delicate meshwork that supplies of oxygen to the peripheral cornea.(9) The limbus has proved to be a reservoir of stem cells (SC), specifically at the limbal palisades of Vogt, where specific anatomical structures termed ‘limbal epithelial crypts’ (LEC) located at the posterior end of some limbal palisades show features of a SC niche.(12,13) The integrity of the corneal epithelium and its ability of self-renewal rely on the existence and viability of a healthy SC population. The latter depends on the existence of a microenvironment characterized by surrounding cells, extracellular matrix (ECM), and growth factors that will finally determine the SC's function.(14) SC's microenvironment and therefore its availability, can be compromised by a large number of congenital and acquired injuries that can result in Limbal Stem Cell Deficiency, characterized by corneal conjunctivalization and vascularization, chronic low grade inflammation, poor corneal epithelium integrity, recurrent erosions or persistent defects/ulcers, basal membrane destruction and fibrous ingrowth.(15)
 
The Tear Film
The tear film is the fluid layer that covers the cornea and the conjunctiva. There are numerous functions of the tear film in the ocular surface and they rely on both, an adequate volume and composition of the tear.(16) One of the primary functions of the tear film is to provide a high quality refractive surface, but also to nurture and protect the corneal and conjuctival epithelium from mechanical insults and dehydration.(17) An adequate tear volume is essential since it will give lubrication and avoid the shear forces generated during blinking.(18) The quality and stability of the tear film is as important as volume, since it will allow a confluent and uniform coverage on the ocular surface.
The three-layered tear film described by Wolff in 1946, has been universally accepted with some modifications.(18) A basal mucin layer produced mainly by the goblet cells of the bulbar conjunctiva (nasal bulbar conjunctiva is the site with a major density of goblet cells) enhances the adhesion of the tear film to the ocular surface through its interaction with the 3glycocalyx created by microvilli of the conjunctival and corneal epithelium generating a hydrophilic environment. Other minor cells distributed all over the bulbar conjunctiva and fornixes are also responsible of producing mucin, such as the Glands of Henle, the Glands of Manz and even some conjunctival epithelial cells.(19) The mucin layer in addition to act as an anchor and hydrophilic surface for the tear film is also thought to act as a mechanic buffer during blinking and as an immunoglobulin reservoir.
The aqueous layer of the tear film is by proportion the grater component, being 98% of the total thickness of the tear film (approximately 6-7µm). It is produced primarily by the lacrimal gland, and in a minor proportion by the accessory lacrimal glands (Krause and Wolfring) located of the fornix and tarsal conjunctiva.(18, 20) The contents of the aqueous layer besides water, are ions (Na+, K+, Mg2+, Ca2+, SO42−, PO42−, HCO3), secretory proteins (IgA), secretory proteins from granules (lysozyme, lactoferrin, peroxidase, lipocalin), other proteins (IgE, serum albumin, pre-albumin) and other nutritional factors (vitamins A, C and E, substance P, epidermal growth factor, transforming growth factor β1/ β2, α1-antitrypsin).(2123) The comprehensive composition of the aqueous tear film speaks in favor of its biochemical, biophysical and bacteriostatic activity. It also plays an important role in creating an osmotic gradient and in controlling the cornea-tear film water influx, as well in maintaining the tear film pH (7.2 − 7.6 when the eyes are open, 6.8 while they are closed).(21)
The lipid layer is thought to be the outermost layer of the tear film. It is formed primarily by the lipid secretion from meibomian glands, but also from other minor modified sebaceous glands such as the glands of Zeiss and Moll.(24) The function of the lipid layer is to retard or decrease the evaporation of the tear film during exposure, to act as surfactant and distribute evenly the tear on the ocular surface, to prevent the tear film contamination with lipids from the skin and to prevent tears from spilling over the eyelids.(22)
More recent evidence has suggested that the trilaminar conventional model may not be correct. Laser interferometry, in vivo cryofixation and reflectance spectra studies suggest that the mucous and aqueous layer should not be considered as different layers but as phases of the tear film, since the presence of a mixed gel layer rather than a pure aqueous layer has been shown to exist.(20, 25)
 
Lid Margin Disease
 
Blepharitis
 
• General Overlook
Any inflammatory process of the lids or the lids borders is called blepharitis. As an inflammatory process is one of the most common conditions affecting patients in the clinical practice in ophthalmology, with a prevalence of 37%-47%.(26) Historically, Thygeson classified blepharitis in two general categories: 1) squamous blepharitis characterized by hyperemia of the lid margin and dry or greasy scales; and 2) ulcerative blepharitis, characterized by small pustules in the base of the eyelashes that later lead to the formation of ulcers.(27) Conjunctivitis and superficial keratitis was common in both types of blepharitis. This classification was soon after modified by Thygeson himself, who recognized the influence of Staphylococcus infection and underlying sebaceous glandular disease in the development of blepharitis. Therefore, he divided the disease in seborrheic, staphylococcus and mixed (seborrheic/staphylococcus) blepharitis.(27)
 
• Evaluation and Classification
The more accepted and used terminology in blepharitis nowadays, is that dividing blepharitis form marginal blepharitis to differentiate the latter as a localized inflammation of the lid margin including both anterior and posterior blepharitis (taking the gray line as a separating anatomical structure).(28) Anterior blepharitis is the inflammation concentrated around the lashes, characterized by debris and collarettes (Figure 1); while posterior blepharitis describes the inflammation posterior the lid margin (Figure 2), usually as a consequence of meibomian glad dysfunction (MGD) but having also other etiologies (acne rosacea, allergic on infective processes).(28) Finally, MGD is defined as a chronic, diffuse abnormality of the meibomian glands, commonly characterized by terminal duct obstruction and/or qualitative/quantitative changes in the glandular secretion.
4
zoom view
Figure 1: Anterior blepharitis. Debris and collaretes on the base of the eyelashes.
zoom view
Figure 2: Severe obstructive-cicatricial Meibomian gland dysfunction in a patient with ocular cicatricial pemphigoid.
It may result in alteration of the tear film, symptoms of eye irritation, clinically apparent inflammation, and ocular surface disease.(28)
Although the acute infection of the eyelid margin, usually located on the glands and generally of bacterial origin (Staphylococcus) manifested as hordeolum is common in the ophthalmological practice, the more problematic entity is chronic blepharitis; a multifactorial disease whose etiology is still not well understood.(1)
Meibomian gland dysfunction (MGD) is recognized as an important component of the chronicity of blepharitis and as the main obstacle for the successful treatment. Likewise, MGD is known to be the first cause of evaporative dry eye.(26) MGD is generally classified in two groups: obstructive and seborrheic disease.(29,30) Obstructive disease is characterized by condensation of meibomian lipids and hyposecretion of lipids to the tears, while seborrheic disease is characterized for an excessive release of oil.(29, 30) Although a large number of classifications to describe and categorize MGD have been published, all of them coincide in that there is a complex interaction between the meibum composition (presence of free cholesterol, cholesterol esters and saturated fatty acids), bacterial overpopulation (S. aureus and P. acnes) and other bacterial overgrowth associated phenomena as augmented bacterial lipase/esterase activity, the release of exotoxins and pro-inflammatory cytokines and other chemoattractants.(27) All these are apparently a regular finding in a minor or major degree in every case of chronic blepharitis, and are associated with other inflammatory conditions as chalazia, rosacea and seborrheic dermatitis.(31)
In an effort to create a consensus over the classification of MGD, in 2011 The International Workshop on Meibomian Gland Dysfunction was created.(28) This classification distinguishes among the subgroups of MGD on the basis of the level of secretions and further subdivides those categories by potential consequences and manifestations. On the basis of these proposed classifications, obstructive MGD is the most pervasive (Figure 3).
 
• Treatment Approaches
One of the oldest and more effective treatments for blepharitis is lid scrubs and lid hygiene.(31) Cleansing of the lids with diluted solutions of baby shampoo or other alkaline solutions (some of them commercially available) are beneficial in removing debris and scaling from the lid margin, hence reducing the inflammatory stimuli.(32) Massage on the lid margin to express the meibum from the glands, has shown to be an effective measure in chronic blepharitis when obstructive MGD is present.(32)
Given that bacterial microorganisms (S. aureus) have been implicated as primary or secondary offenders in blepharitis, the control of these infectious agents 32) should be an initial step in the management.(26, 32) Although antibiotics will not control chronic blepharitis alone, short courses of antibiotic (5 to 7 days) using erythromycin, polimixin or bacitracin ointments have proved to be efficient in reducing symptoms when clinical findings suggest bacterial overgrowth.(29) Recently, the use of topical solutions or ointments of azithromycin has proved to be effective in reducing symptoms and signs in chronic blepharitis.(33, 34)
5
zoom view
Figure 3: Meibomian Gland Dysfunction Classification. Reproduced from Nelson et al, IOVS Spcecial Issue 2011; 52(4): 1931-1937.
Azithromycin efficacy in treating blepharitis has been attributed to both, its broad-spectrum anti-bacterial profile and to its antiinflammatory properties.(34)
The use of systemic tetracycline has proved to be effective in reducing the bacterial lipase activity, in altering the composition of meibomian gland secretion (reducing the free fatty acids production) and as antiinflammatory drugs, since they act as anti-chemotactic agents.(35, 36) The use of low doses of tetracycline or minocycline for two months and posterior taper over a longer period has proved to be beneficial in treating blepharitis.(36)
Other nutritional supplements as linoleic and linolenic essential fatty acids have shown to be effective in reducing symptoms and signs of chronic blepharitis. Theoretically, they would act modifying the composition of the meibomian gland secretion and modulating inflammation.(37)
 
Ocular Rosacea
 
• General Overlook
Rosacea is a chronic inflammatory disease of the skin and the eyes affecting approximately 10% of the adult population.(38) The dermatologic disease was identified in 1367 by Chaucer, but the ophthalmologic manifestations were recognized until 1864 by Arlt and Wise.(39)
6
It is a disease prevalent in adults between 30 and 50 years old, and it does not have a gender predilection.(40, 41) Up to 50% of the patients with rosacea have some degree of eye disease.(40) Even though it is generally a disease known to affect adults, childhood rosacea has been reported with a relatively higher frequency in the last years.(42) Some authors argue that the low rate of ocular complications and the mild treat of the dermatologic manifestations, as well as the lack of expertise in identifying the clinical patterns in pediatric population are the cause of under-diagnosis.(42) Rosacea is a disease with a higher prevalence in fair-skinned people, but this could be misleading since it is known that patognomonic dermatological sings are easily masked in dark skin population, hence diagnosis is often more complicated in these patients.(40)
The etiology and pathogenic mechanisms of rosacea are not totally clear.(41) The isolation of Staphylococcus aureus from skin of patients led to think that bacterial microorganisms were the primary etiology of rosacea.(40) However, up to 50% of the cases of typical rosacea had negative cultures and biopsies; therefore the role of bacteria as a secondary hallmark and not as primary etiology was considered.(43) The role of actinic damage and exposure to temperature changes (hot or cold) have also been implicated in the pathology of this disease, since all of them exacerbate the cutaneous symptoms.(40) Bernsterin and Soltani observed that endorphin release originated by ethanol produced a flush reaction in patients with rosacea.(44) They concluded that these patients may produce a large quantity of endorphins, be highly sensitive or have an increased number of endorphin receptors. Recently, Li et al. showed a direct relation between Demodex folliculorum infestation, serum immunoreactivity to Bacillus oleronius antigens and rosacea, suggesting a possible role in the etiology and pathogenic mechanisms.(45) Finally, an increased matrix metalloproteinase activity has been observed in patients with rosacea, justifying the use of tetracycline and other inflammatory modulators in this disease.(43)
 
• Evaluation
Dermatologic and ophthalmologic manifestations of rosacea are summarized on Figure 4. Skin manifestations include flush areas on the forehead, cheeks, chin, nose and the “V” area of the neck and chest.(40) Phymatosis of the tissues, specially the nose, is a hallmark of the chronicity of the disease.(46) Corneal manifestations are the most prevalent in the group of patients with ocular rosacea, and they are usually related to significant visual loss.(46) They include punctate keratopathy, marginal vascular infiltration, peripheric ulcerative keratitis, corneal scarring and thinning. Other less common ophthalmologic manifestations of ocular rosacea include episcleritis, pseudokeratoconus, dendritic keratopathy, cicatricial conjunctivitis and it has also been associated with bilateral herpetic keratitis.(47) Blepharitis, meibomitis and the presence of telangectasias on the eyelid margin are also distinctive features (Figure 4).(47)
zoom view
Figure 4: Rosacea Clinical Manifestations.
Even though ocular rosacea is always bilateral, it is often asymmetrical.(43) The dermatologic signs of rosacea generally precede the ocular signs, but sometimes the former are so mild that rosacea can debut as an apparent primary ocular rosacea. In patients with both ocular and dermatologic manifestations, 20% initially exhibit pure ocular manifestations, 53% exhibit only cutaneous disease and 27% present both.(40)
 
• Treatment Approaches
The treatment of the cutaneous lesions is based on the use of systemic (erythromycin, metronidazole) and/ or topical antibiotics (metronidazole, doxycycline).(48) The treatment of ocular rosacea is directed to control the symptoms and prevent the ocular complications.(42) Most patients with ocular rosacea have some degree of concomitant anterior or posterior blepharitis; hence the use of lid hygiene and scrubs helps to eliminate debris, 7decrease the bacterial biota and to accelerate the lipid secretion exchange from meibomian glands. The use of topical antibiotics as erythromycin or bacitracin, also helps to decrease and avoid the bacterial overgrowth whose lipases/esterase contribute to the production of free fatty acids thus to the alteration of the tear film (decrease in the tear break up time).(32, 49) Topical steroids can be helpful in the management of complications such as episcleritis, sterile keratitis or uveitis, but their use should be cautious and in low doses because of the risk of bacterial or fungal infection.(42)
Significant ocular disease also requires from the use of systemic antibiotics, specifically tetracycline-like drugs. As stated before, they inhibit bacterial lipases, decrease the production of free fatty acids and reduce the production of pro-inflammatory cytokines.(41, 42, 43, 49) Cycles of tetracycline 50 to 100 mg twice a day for one month, and then once a day for one or two extra months have been effective in controlling symptoms and signs of ocular rosacea.(42) In children, low dose erythromycin (50-70% of the usual dose) three to four times a day for periods of 4 to 6 weeks have shown to improve the signs of symptoms of ocular rosacea.(50) Macrolides as well as tetracycline, besides having a broad spectrum antibacterial activity have also an anti-inflammatory profile, inhibiting bacterial lipases, neutrophil chemotaxis and the release of pro-inflammatory mediators.(51)
 
Dysfunctional Tear Syndrome
 
• General Overlook
Previously we discussed the importance of the tear film to preserve the well being of the ocular surface, to provide a high quality refractive surface and to nurture and protect the corneal and conjunctival epithelium. Dysfunctional tear syndrome or dry eye disease is highly prevalent affecting 14% to 33% of the population worldwide depending on the used classification and diagnostic criteria.(5254) Dry eye complaints are the second cause of visit to the ophthalmologist.(55) Although is an overlooked disease, studies analyzing the quality of life with dry eye disease found decreased quality of life for all levels of severity of dry eye syndrome, with an effect of quality of life in severe dry eye syndrome comparable with that reported for moderate angina.(56)
Risk factors for dry eye syndrome are numerous; being the most commonly reported older age, female sex, postmenopausal status, previous LASIK or refractive excimer laser surgery, use of medications (antihistamines) and connective tissue disease.(57) Symptoms reported by patients with dry eye include ocular discomfort and irritation such as scratchiness, grittiness, foreign body sensation, burning, blurring and itching.(58) These symptoms are usually exacerbated by exposure to low humidity environments (air conditioning), prolonged use of video terminals and systemic medications that dry the ocular surface.(59)
Dry eye disease diagnosis and treatment is challenging, since it encompasses several etiologies and varies greatly in severity. It is recognized that the ocular surface and the tear-secreting glands act as a unit and maintain the tear supply at the same time that provide clearance of used tears.(60) Disease or dysfunction of any part of this unit results in a poor quality or quantity of tear film that causes ocular irritation and damage to the surface epithelium (Keratoconjunctivitis sicca or KCS). Disease of the integrated unit can be generated from aging, deficient nutritional or supportive factors (hypo-androgenic state, vitamin A deficit, low dietary intake of omega 3 fatty acids), ocular diseases (herpes keratitis), systemic inflammatory or infiltrative diseases (connective tissue diseases, Sjögren syndrome), ocular surgery or trauma that disrupts the trigeminal afferent sensory nerves (LASIK) or any systemic medication that interfere with a correct stimulation of tear production (antihistamines, any medication with anti cholinergic effect).(60, 61) Finally decreased tear secretion, augmented tear osmolarity and clearance deficiency promotes an inflammatory response in the ocular surface that involves both cellular and soluble inflammatory mediators (Figure 5).(62, 63)
In 2007, a collaborative group of cornea and ocular surface specialists created a definition and classification of dry eye disease as a part of the International Dry Eye Workshop.(64) In this report, participants agreed that the two major factors, deficient aqueous layer production and increased evaporative loss, may cause dry eye independently, but in a considerable percentage of the cases could be present at the same time, contributing to dry eye symptoms and signs. Figure 6 resumes the major etiological causes of dry eye.
8
zoom view
Figure 5: Inflammatory mediators in KCS. Reproduced from Pflugfelder SC. Antiinflammatory therapy for dry eye. Am J Ophthalmol 2004;137:338
zoom view
Figure 6: Major etiological causes of dry eye. Reproduced from Lemp MA (Chair). Definition and Classification Subcommittee of the International Dry Eye Workshop. The definition and classification of dry eye disease: report of the Definition and Classification Subcommittee of the International Dry Eye Workshop (2007). Ocul Surf 2007;5:75-92
 
• Diagnostic Tests and Evaluation
Dysfunctional tear syndrome (DTS) diagnosis and assessment is usually complicated, since correlations between patient symptoms, clinical signs and diagnostics tests are often variable.(65) An accurate and detailed clinical history is mandatory when examining a patient with dry eye complaints: occupation, contact lens use, 9relevant medical (allergy, connective tissue disease, medications) and ocular history (surgery, trauma, topical medications) and detailed description of symptoms (duration, most common complaints, exacerbating conditions).(66)
Generally, patients with dysfunctional tear syndrome share one or more of the following: unstable tear film with a rapid break up time, elevated tear osmolarity and delayed fluorescein clearance. Thus, entry tests to any patient with dry eye symptoms should include tear break up time and fluorescein clearance time, osmolarity test are usually expensive and unavailable, and therefore they are not routinely used.(66)
Tear break up time (TBUT) is evaluated by instilling fluorescein dye the tear film and evaluating the interval between a complete blink and the appearance of the first randomly distributed black dry spot in the precorneal tear film.(67) Other options include noninvasive methods for evaluating the tear film stability include the use of xeroscopes or keratometer to assess the time that a regular pattern (placid rings or grids) takes to distort or break before a blink. Although there is a great variability in tear breakup times in normal subjects, a time of 10 seconds or less for both fluorescein and non-invasive methods, consistently confirms the presence of unstable tear film.(66, 67) Fluorescein clearance test is a test similar to Schirmer test but it evaluates the clearance of the fluorescein dye instilled after use of topical anesthesia. Schirmer strips are inserted every 10 minutes for 30 minutes to evaluate the fluorescein staining in the strip, and at the last test Schirmer strip is inserted after nasal stimulation. Measurements < 3 mm with disappearance of dye at 15 minutes or with delayed clearance (>15 min without nasal reflex) suggests aqueous tear deficiency, while measurements > 3 mm without dye clearance suggest delayed tear clearance.(68)
The most used test to diagnose aqueous tear deficiency is the Schirmer test. It can be used with or without anesthesia, the latter known as Schirmer 1.(66) A Schirmer 1 test with < 5.5 mm of strip wetting at 5 minutes is considered diagnostic of aqueous tear deficiency by Van Bijsterveld (sensitivity of 83%).(69) Jones popularized the Schirmer 2 test (with topical anesthesia) to measure the basal tear secretion, considering abnormal a value of < 10 mm of strip wetting at 5 minutes.(70) From there, patients with aqueous tear deficiency could be further classified as Sjögren or non-Sjögren depending of the presence of other systemic findings (dry mouth, dry skin, dysphagia, arthritis) and a positive biopsy and/or antibody titer (SS-A and SS-B).(66)
Finally the diagnostic dye staining using fluorescein, Rose Bengal or lisamine green is used to detect the severity of the ocular surface disease associated with dry eye (KSC).(67) Different scales of disease severity have been published, grading the severity of the disease depending on the extension, localization and coalescence of the epithelial staining. Two of the most used scales are the Van Bijsterveld scale(69) and the SICCA score (Table 1) the latter was found to have a high correlation when compared with the labial salivary gland biopsy focus scores and the anti-SS-A/-B serology in the diagnosis of primary Sjögren Syndrome.(71, 72)
However, the correlations between the result of these diagnostic tests, patient's symptoms and the clinical signs observed by the ophthalmologist are often misleading. In order to address this problem and to create more effective treatment algorithms, an International Task Force (ITF) consisting of 17 dry eye experts clinicians was impaneled in 2007.(65) The panel agreed that disease severity was the most important factor in treatment decision making and that patient's signs and symptoms were key in determining DTS severity, with less reliance on diagnostic tests such as Schirmer test. In general, they divided DTS in two categories: with and without lid margin disease. At the same time and for treatment purposes, they classified the DTS without lid margin disease in a scale of severity consisting on four levels (Table 2).
 
• Treatment Approaches
In short the ITF, based on the Delphi Approach to Treatment Recommendations, suggested treatment with lid hygiene and topical antibiotics for patients with DTS with anterior lid margin disease; and treatment with lid scrubs/local hyperthermia/massage, systemic tetracycline and topical steroids for patients with DTS with posterior lid margin disease.(73) In the case of DTS without lid margin disease, physicians determined each patient's dry eye severity level by using the ITF guidelines presented in Table 3A and from there established the guidelines for treatment at each severity level (Table 3B).
10
Table 1   SICCA (Sjögren International Collaborative Clinical Alliance) ocular staining score form. (Reproduced from: Whitchers PJ, et al. A Simplified Quantitative Method for Assessing Keratoconjunctivitis Sicca From the Sjögren Syndrome International Registry. Am J Ophthalmol 2010; 149: 405-415.)
zoom view
Table 2   Three major subsets found in DTS. (Reproduced from Behrens A, et al. Dysfunctional Tear Syndrome, A Delphi Approach to Treatment Recommendations. Cornea 2006;25:900–907.)
zoom view
11
Table 3A   ITF Guidelines for Determining the Severity Level of DTS.(73)
Table 3A
DTS Severity
Level 1
Level 2
Level 3
Level 4
Symptoms*
Mild - moderate
Moderate - severe
Severe
Severe
Signs†
Mild - moderate conjunctival signs
Tear film signs Fluctuation of vision / blurred vision
Corneal filamentary keratitis
Corneal erosions Conjunctival scarring
Staining†
None
Mild punctate corneal staining Conjunctival staining
Central corneal staining
Severe corneal staining
*Ocular discomfort, ocular fatigue, and visual disturbance each ranked on a scale of 0 (none) to 4 (extremely severe).
†Graded on a scale of 0 (low) to 4 (high).
Table 3B   ITF Guidelines for Treatment of DTS at Each Severity Level.(73)
Table 3B
DTS Severity
Level 1
Level 2
Level 3
Level 4
Treatment Options
Patient education
Unpreserved tears
Oral tetracycline
Systemic antiinflammatory
(without lid margin disease*)
Environmental modification
Gels, ointments
Punctal plugs (after inflammation has been controlled)
Acetylcysteine
Preserved tears
Topical cyclosporin A
Moisture goggles
Control allergy
Topical steroids Secretagogues Nutritional support
Surgery (tarsorrhaphy)
Treatment algorithm
If no improvement, add level 2 treatment
If no improvement, add level 3 treatment
If no improvement, add level 4 treatment
*For patients with lid margin disease, the guidelines include the above treatments plus one or all of the following: lid hygiene, thermo-massage, oral tetracycline.
Evidence suggest that the use of the ITF recommendations has led physicians to treat earlier stages of TDS more effectively, to rely more on patients symptoms rather than just on diagnostic tests and since ITF guidelines recommend escalation of treatment to the next level if no improvement occurs, physicians were more likely to use topical cyclosporine and topical steroids.(73) The use of these latter, accordingly with the evolving understanding of the dry eye pathophysiology, might as well interrupt the vicious inflammatory cycle an prevent the progressive damage.
Other modality approaches have been used in cases of severe dry eye and KCS refractory to conventional treatments. Specifically, the use of autologous serum drops at different concentrations (ranging from 20% to 100%) has proved to be effective in improving dry eye both clinically and subjectively.(74) The effect of autologous serum has been attributed to the presence of epidermal growth factor (EGF), fibronectin, basic fibroblast growth factor (bFGF), vitamin A and anti-proteases that would finally aid in modulating the inflammatory response and improve ocular surface health.(74)
12
 
Ocular Surface Squamous Neoplasia
 
 
• General Overview
Ocular surface squamous neoplasia (OSSN) is a term that embraces a wide spectrum of conjunctival, limbal and corneal lesion of squamous origin.(75, 76) The pathologic involvement of the lesion can be from mild to moderate dysplasia, to full thickness epithelial dysplasia (carcinoma in situ) and invasive squamous carcinoma.(76)
Although relatively uncommon and the classic behavior invariably depicts a slow growing, prompt clinical diagnosis, histopathological correlation and treatment are essential in OSSN since they do have the potential for intraocular or orbital invasion, distant metastases and death, especially in neglected cases.(77)
OSSN incidence is low, reported from 1.9/100,000 population in Australia(78) to 0.3 cases per million per year in the US.(79) Some risk factors for the development of OSSN have been identified. It occurs predominantly in older men, with a predilection for occurrence between the fifth and sixth decade of life (average age 56, range from 4 to 96 years).(75) Of importance, in the older population OSSN is the third most common ocular tumor after melanoma and lymphoma.(75) Racial predilection for Caucasian men has also been observed, with a predominance ranging from 90% to 100% and a rate of OSSN fivefold higher.(80, 81) Interestingly, a correlation between the age of onset and the geographical distribution has also been reported. A younger onset of OSSN has been observed in persons nearer to the equator (latitudes less than 30 degrees), at the same time that a decrease of 49% in the rate for squamous cell carcinoma was observed for each 10 degree increase in latitude.(82, 83)
Hence, ultraviolet B (UV-B) radiation has been strongly related with OSSN.(84, 85) Direct DNA damage, mutagenic changes in specific oncogenes (p53) and failure of DNA repair (xeroderma pigmentosum) have been proposed to play a key role in OSSN etiopathogenesis/oncogenesis.(76, 83, 86, 87)
A direct relationship between ocular squamous neoplasia and human papilloma virus (HPV) types 16 and 18 has been demonstrated.(88) A narrow molecular association between HPV and proteins encoded by the p53 suppressor gene on the host has also been reported, suggesting a crucial role of HPV in the pathogenesis of OSSN.(88) Other less studied but reported risk factors include: heavy tobacco smoking, exposure to petroleum products, extended or chronic ocular surface disease and exposure to chemicals as arsenicals or beryllium.(76)
 
• Classification and Histological Features
Ocular surface squamous neoplasia is classified depending on the degree of histological dysplastic changes (thickness of the involved epithelium) and the extent of invasion. OSSN can be classified in benign, preinvasive and invasive (Table 4).(76) Thus in preinvasive OSSN, mild dysplasia (Grade I) is characterized by atypical cells invading less than one third of epithelial thicknesss.(89) In moderate OSSN (Grade II),atypical cells occupy from one third to two thirds of the epithelial thickness and in severe OSSN (Grade III) epithelium exhibits near total thickness atypical changes (Figure 7).(89)
Squamous carcinoma typically shows nests of infiltrative cells that break through basement membrane and invade conjunctival stroma (Figure 8).(89)
Table 4   Classification of ocular surface squamous neoplasia.
Table 4
Benign
Preinvasive
Invasive
Papilloma
Pseudotheliomatous hyperplasia
Benign hereditary intraephitelial dyskeratosis
Conjunctival/corneal intraepithelial neoplasms grade II-III
Squamous carcinoma
Mucoepidermoid carcinoma
(Adapted from Basti S, Macsai MS. Ocular Surface Squamous Neoplasia. Cornea 2003;22:687–704)
13
zoom view
Figure 7: Ocular surface squamous neoplasia. Conjunctival Intraepithelial Neoplasia with moderate dysplasia (Grade II), showing characteristic tufts of blood vessels and papilliform appearance.
zoom view
Figure 8: Squamous carcinoma invading clear cornea, showing a nodular appearance.
Neoplastic histological features are consistent with faulty maturational sequencing characterized by hyperchromatic atypical nuclei, scant cytoplasm and mitotic figures.(81)
 
• Clinical Features and Diagnostic Ancillary Tools
Although many macroscopic features of the squamous neoplasia of the eye have been described, they all share some distinctive traits that help in the clinical diagnosis. In general, they consist on elevated lesions with characteristic tufts of blood vessels and a pearly gray appearance.(90) Usually they are restricted to the conjunctiva, may sit astride the limbus and seldom invade the clear cornea. The gross appearance of the lesions has been described as one of the following: leukoplakic, gelatinous, papilliform, nodular or diffuse.(76, 91) The gelatinous variety is the most commonly described, and the nodular type has been reported to have the most malignant behavior, with rapid growth and spread to the lymph nodes.(76)
Corneal OSSN is typically differentiated for being circumscribed opalescent ground-glass lesions with well defined and fimbriated borders.(76) They are described generally as pre-invasive, have a slow growth, tend to be indolent and tend to have a high recurrence rate.(76, 92) Clinically, they have a dysplastic gray epithelium that stains diffusely with Rose Bengal (Figures 9, 10) and can be readily appreciated by retro illumination.(76)
Benign lesions often are exophytic, papillary red colored lesions with notable fibrovascular core.(76) They are very common in childhood and are prone to be multiple and pedunculated, localized on the fornix, caruncle or eyelid margin.(76) In adults they tend to be single, sessile and confined to limbus or conjunctiva.
Even when some traits as rapid spread or growth and fixation to deep ocular structures may suggest malignancy, it is often impossible to differentiate clinically benign lesions from pre-invasive or invasive ones.(93) Clinical diagnosis alone has proven to be accurate only in 40% of the cases of OSSN, even in the hands of experienced physicians.(75)
Therefore, diagnostic tests are usually required before treatment. They include excision biopsy in small lesions, incisional or map biopsies in larger lesions and cytology.(76)
zoom view
Figure 9: Ocular surface squamous neoplasia showing staining with rose bengal.
14
The latter has been shown to be an effective method for diagnosis, evaluation during medical treatment and follow up after treatment.(94) Techniques described for cytology include exfoliative cytology (through a platinum spatula, cytobrush or sampling by aspiration with a tuberculin syringe) and impression cytology.(95) The use of Biopore membrane for impression cytology (Millicell-CM, 0.4 μm PICM 012550, Millipore Corp, Bedford, MA) instead of cellulose paper, proved to be very good method for obtaining and harvesting ocular surface cells and to provide a more mechanically stable transport medium, being able to be placed in 95% alcohol for several weeks before processing.(96) Described cytology features in pre-invasive OSSN are keratinized dysplastic cells (55%), syncytial –like groupings (35%), non-keratinized dysplastic cells (10%). Invasive squamous cells carcinoma samples in the other hand showed abnormal keratinization (70%), but even experienced pathologist cannot predict invasion based on impression 97) cytology.(94, 97)
Recently, Ultra-High resolution (UHR) OCT showed to be a reliable non invasive diagnostic tool to evaluate ocular surface lesions.(98) It demonstrated a statistically significant difference in epithelial thickness and a significant degree of morphologic correlation with the histopathologic results when evaluating OSSN and pterygium. The potential use of UHR OCT for diagnosis, joined to the capability of using it for patient follow-up during the course of medical treatment and continued surveillance for neoplasia without mandatory repeated biopsies, makes it a very promising and valuable diagnostic tool.(98)
 
• Treatment Approaches
The gold standard for managing lesions suspected of OSSN, has historically consisted on surgical excision, with evolving trends from simple excision(75) to Shield's “no touch” technique,(99) increased surgical margins (3-4 mm) and intraoperative adjuvant agents including cryotherapy (double freeze-slow thaw),(99, 101) absolute alcohol,(99, 102) mitomycin C (MMC)(103) and ocular surface reconstruction with amniotic membrane instead of primary closure (Figure 10, A and B).(102) Even when it is difficult to compare recurrence rates between series using the last combined surgical approach, it appears that these newer techniques offer decreased tumor recurrences (reported as low as 5%) compared with the previously reported in literature (recurrence rate of 15% to 52%).(80)
zoom view
Figure 10: A. Squamous carcinoma, showing elevated nodular appearance, augmented tufts vessels and corneal invasion. B. Postoperative day 1 of excisional biopsy with “No touch” technique, using cryotherapy, absolute alcohol and amniotic membrane for ocular surface reconstruction.
Topical chemotherapy for OSSN with agents mitomycin-C (MMC), 5-fluorouracil (5-FU) and interferon-a2b (IFN-a2b) have shown to be effective in reducing and completely eliminating the lesions,(104) even in cases of giant OSSN (median diameter 20 mm, median 6 clock hour extension).(105) Although there are no randomized clinical trials directly comparing the previous mentioned chemotherapeutic agents, published studies indicate equal efficacy of these agents for the treatment of non-invasive OSSN (80% − 88%).(104) Topical chemotherapy offer advantages over the classical excision and cryotherapy approach. Importantly, topical therapy delivers treatment not only to the affected surface, but to the entire ocular surface eliminating potential subclinical OSSN.(106)
15
Table 5   Relative indications for topical chemotherapy in non invasive OSSN
Table 5
1
>2 quadrants of conjunctival involvement
2
>180º of limbal involvement
3
Extension to clear cornea with involving pupillary axis
4
Positive margins after surgical excision
5
Patient unable to undergo surgery
(Adapted from Sepulveda R, Pe'er J, Midena E, et al. Topical chemotherapy for ocular surface squamous neoplasia: current status Br J Ophthalmol 2010 94: 532-535)
Also has a superior cost-effective profile, is associated with reduced patient morbidity and eliminates the risk of iatrogenic limbal stem cell deficiency.(107, 108) Relative indications for topical chemotherapy in OSSN are summarized in Table 5.
Treatment schemes wit 5 FU (a pyrimidine analogue) as 1% topical solution, applied four times a day in cycles of 4 days “on” and 30 days “off” until resolution of the lesion have shown to be effective in 87% to 93%.(109, 110) Commonly reported adverse effects include conjunctival and corneal inflammation, corneal epithelial defects and eyelid skin erythema.(111)
MMC, classified as an alkylating agent, has been used widely in concentrations ranging from 0.02% to 0.002% as topical solutions.(104) It has been used as primary chemotherapy, as adjuvant intraoperatory treatment to reduce postoperative recurrences(103) and postoperatively after recurrences. Overall, its excellent response rates ranging from 87.5% to 100% have been reported.(104) The most widely used protocol uses MMC 0.02% four times a day in cycles of 1 or 2 weeks (ranging from 1 to 5 cycles, average 2 cycles) with a free interval of 1 week until resolution of the lesion.(112) It should be used with an intact epithelium to decrease the risk of corneal or scleral melting. Some reported adverse effects include conjunctival hyperemia, corneal erosions, punctal stenosis and stem cell deficiency when applied in concentrations.(113)
Interferon (IFN) α2β, a recombinant glycoprotein used in the treatment of Hepatitis B and C, hairy leukemia and HIV, has proven to be highly effective in the treatment of non-invasive OSSN.(114) Interferon is reported to be effective in treating and regressing OSSN in 80% to 96.4% of the cases, with resolution of the lesion often requiring from two to three months of continuous treatment.(115) The typical dose of IFN α2β given topically is 1 million UI/ml four times a day. Higher doses of 3 million UI/ml showed to be also effective but not significant different from that of 1 million UI/ ml, with trends toward more side effects in higher doses.(116) Common reported side effects are consistent with transient follicular conjunctivitis and corneal epithelial cysts.(107,111) Subconjunctival application or higher doses are associated with systemic symptoms as fever, myalgias and fatigue.(116)
A suggested algorithm for management and follow up of OSSN is depicted in Flow Chart 1. Enucleation should be considered as the treatment of option in patients with advanced disease, with evidence of invasion through limbus to intraocular structures.(99, 117) Likewise, exanteration is to be pondered with evidence of orbital invasion such as, extensive forniceal spread, perineural or orbitary septum invasion.(99, 117)
 
Autoimmune Cicatricial Conjunctivitis
 
Ocular Cicatricial Pemphigoid
Mucous membrane pemphigoid (MMP) is a systemic autoimmune disease, characterized by subepithelial blistering, scarring and shrinkage of mucosal membranes.(118, 119) When the clinical findings are primarily seen on the conjunctiva, the disease is called ocular cicatricial pemphigoid (OCP) or mucous membrane pemphigoid with ocular involvement (MMPO).(120)
16
zoom view
Flow Chart 1:
17
When ocular involvement occurs (approximately 80% of the patients with MMPO), bilateral sight-threatening disease may progress if untreated, since progressive conjunctival cicatrization, corneal neovascularization and scarring is a constant feature.(121, 122) It is important to realize that, as a systemic disease, most of the systemic manifestations occur at extraocular sites: oral mucosa, esophagus, larynx and skin.(119) Desquamative gingivitis is one of the most common mucosal clinical findings, present in 65% of patients.(121)
Even when MMPO is thought to be a rare disorder, with incidences ranging from 1 in 12,000 to 1 in 60,000, underestimation of the real incidence is proposed since reports concentrate in patients with more advanced disease.(119, 123) The average age of patients vary between 65 and 70 years.(119, 124)
MMPO is described as an autoimmune disease exhibiting the deposition of IgG, IgA, IgM, and/or complement (type II Gell-Coombs hypersensitivity reaction) in the epithelial basement membrane zone (BMZ).(119,123) A genetic predisposition was found in patients with HLA-DQβ1*0301 gene imbalance.(125) A specific auto antigen localized in the basement membrane, the β4 subunit of α6β4 integrin, has been identified as a target for autoantibodies in MMPO.(126) Subsequent activation of the complement cascade at the level of the lamina, inflammatory cell recruitment (plasma cells, neutrophils, lymphocytes and mast cells), cytokines and lytic enzymes release ends up in subepithelial bulla formation, fibroblast activation and scarring.(119)
Early clinical ocular findings are consistent with unilateral chronic follicular conjunctivitis that slowly progresses to involve (often asymmetrically) both eyes.(118) For clinical purposes, two major classifications have been described and used, one proposed by Mondino and Brown and the other by Foster.(119) The former describes the diseases based of the severity of forniceal shortening: Stage I has less than 25% shortening, Stage II between 25% and 50% shortening, Stage III 75% and Stage IV 100% or end stage cicatricial stage.(127) In the latter described by Foster, MMPO stage 1 depicts chronic conjunctivitis with subepithelial fibrosis (Figure 11); stage 2 shows foreshortening of the inferior fornix (Figure 12); stage 3 is characterized by symblepharon formation (Figure 13) and finally severe ocular surface keratinization, absence of inferior fornix and corneal vascularization is seen in stage 4.(128)
Eyelids show a variety of alterations in advanced disease. Changes consisting in keratinization of the mucocutaneous junction, eyelash misdirection (trichiasis) and eyelid position disturbances (entropion or lagophthalmos) further complicate and perpetuate the damage in the ocular surface.(119)
Severe dry eye is frequent in later stages of the disease. Chronic keratinization and ocular surface scarring results in occlusion of the main and accessory lacrimal ducts, meibomian gland obstruction and goblet cell depletion with a consequent deficiency in the production of the three layers of the tear film.(119, 127) Corneal changes consisting of erosion (Figure 14), ulceration, neovascularization, keratinization and perforation result from a combination of multiple factors (mechanical trauma, corneal scarring and neovascularization, tear film deficiency, eyelid and eyelashes alterations and conjunctival scarring).(123)
zoom view
Figure 11: Mucous membrane pemphigoid with ocular involvement. Subepithelial fibrosis (Stage I Foster).
zoom view
Figure 12: Mucous membrane pemphigoid with ocular involvement. Fornix shortening (Stage II Foster).
18
zoom view
Figure 13: Mucous membrane pemphigoid with ocular involvement. Symblepharon formation (Stage III Foster), initial keratinization of conjunctiva can be appreciated.
The diagnosis of MMPO is often delayed, since initial symptoms are non-specific and often a misdiagnosis of chronic or recurrent conjunctivitis made.(121) Foster et al observed that 86% of the patients with diagnosis of MMPO, presented in later stages of the disease (stages III or IV of Foster classification).(118) Thus, early diagnosis is essential for delaying or preventing late stages complications. Differential diagnosis to rule out when seen a patient highly suspicions of ocular cicatricial pemphigoid, include all the diseases causing cicatricial conjunctivitis (Table 6).
The gold standard for the diagnosis of MMPO is direct immunofluorescence (DIF).(129) Staining of the conjunctival tissue and visualization of the linear deposition of immnunoreactants (IgG, IgA, IgM and C3) along the epithelial BMZ makes the diagnosis.(129) Direct immuno-electron microscopy (DIEM), is an immunopathologic technique based on the electron microscopic detection of peroxidase-labeled antibodies that are attached to the autoantigens of the BMZ.(130) DIEM has proved to be a more sensitive test than DIF and also is able to precisely locate the immune complex deposits in the BMZ, allowing a more accurate differentiation between MP and other immune-mediated bullous disorders, including bullous pemphigoid, epidermolysis bullosa acquisita and linear immunoglobulin A (IgA) disease.(130) However, DIEM is usually a more sophisticated, not widely available, and time consuming technique, then is not routinely used.
zoom view
Figure 14: Mucous membrane pemphigoid with ocular involvement. Meibomitis, severe corneal neovascularization in 360º and a persistent epithelial defect are shown.
The evidence suggests a correlation between the level of titers of IgG anti– basement membrane zone antibodies at initial presentation with disease activity and predict disease severity.(131)
Ocular complications derived from MMPO that can be managed medically, should be aggressively addressed. Dry eye syndrome and blepharitis should be intensively managed with lubricants, punctal plugs or cauterization and lid hygiene and antibiotic treatment respectively. Eyelid issues as entropion, ectropion or distichiasis can be surgically managed only when inflammatory control of the disease is achieved.(119)
Because the risk of blindness, systemic immunosuppressive treatment is mandatory in MMP with ocular involvement.(129) Systemic treatment with prednisone and cyclophosphamide (a nitrogen-mustard-derived alkylating agent) or alternatively with azathioprine and dapsone has been recommended.(132) Although related with systemic side effects (infections, hematuria and anemia the most commonly reported), the use of cyclophosphamide and prednisone was strongly related with the development of ocular remission (86.3% of the patients with remission at some point during the first year of treatment).(132) The initial recommended dose of cyclophosphamide was 2 mg/kg/day in combination with prednisone 1 mg/kg daily. The prednisone is tapered over 3 or 4 months, whereas the cyclophosphamide is continued for a total of 12 to 18 months of therapy.(122)
Observational studies have also suggested the efficacy of other systemic immunosuppressants as azathioprine, methotrexate, sulfasalazine, mycophenolate mofetil and intravenous immunoglobulins (IVIg) in preventing the progression of ocular disease.(133136)
19
Table 6   Causes of Cicatricial Conjunctivitis.
Table 6
SYSTEMIC BULLOUS DISEASES
Toxic epidermal necrolysis (TEN), epidermolysis bullosa, acquisita, pemphigus vulgaris
MEDICATION-INDUCED
Systemic: practolol, D-penicillamine
Topical: epinephrine, echothiophate iodide, pilocarpine, idoxuridine
INFECTIOUS
Bacterial: Corynebacterium diphtheriae, Beta-hemolytic streptococcus, Neisseria gonorrhea
Viral: Adenovirus, Herpes simplex conjunctivitis
Chlamydia: Trachoma, Lymphogranuloma venerum
TRAUMA
Chemical burns, thermal burns, mechanical trauma, radiation damage, conjunctival surgery, carotid-cavernous fistula
AUTOIMMUNE
Ocular cicatricial pemphigoid, Stevens-Johnson syndrome, graft-versus-host disease, progressive systemic sclerosis, systemic lupus erythematosus, Sjögren's syndrome, Wegener's granulomatosis, sarcoidosis
CONJUNCTIVAL
Atopic blepharoconjunctivitis, ligneous conjunctivitis, rosacea blepharoconjunctivitis, other causes of infectious membranous conjunctivitis
(Reproduced from Kirzhner M, Jakobiec FA. Ocular Cicatricial Pemphigoid: A Review of Clinical Features, Immunopathology, Differential Diagnosis, and Current Management. Semin Ophthalmol, 26(4-5), 270–277,2011)
However, these studies are in general limited by the small size sampling, short follow-ups and inconclusive data regarding the control of ocular inflammation. Recent evidence showed that the combination therapy of Rituximab (a chimeric monoclonal antibody against the protein CD20 found in the surface of B cells) and IVIg arrested disease progression and prevented total blindness in patients with recalcitrant OCP.(137) Concerns with the latter involve the high incidence of systemic infections, which sometimes leads to fatal septicemia.(138)
Since systemic immunotherapy requires strict and frequent systemic workup (renal and liver function tests, complete blood counts, glucose-6-phosphate dehydrogenase), MMPO treatment is best accomplished by a team of specialized physicians with experience in the administration of immunomodulatory agents.(119) Therefore, collaborative work from a rheumatologist or oncologist and an ophthalmologist is preferable.
 
Stevens-Johnson Syndrome
 
• General Overlook
Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are severe immune mediated, life-threatening skin reactions attributable to drugs.(139) These two conditions are closely related and are considered a spectrum of epidermal bullous disease of increased severity and mortality.(140) Both are characterized by erosions of mucous membranes as well as widespread destruction and detachment of the epidermis.(141) SJS or erythema multiforme major is a skin condition characterized by widespread macules and atypical target lesions with epidermal detachment and mucous membranes erosions that involves < 10% of body surface area (BSA).(142) TEN is a more severe and extensive disease involving > 30% of BSA and is described to have large confluent blisters with epithelial detachment, as well as skin and mucous membrane erosions. Overlapping disease (10% to 30% of BSA) is described as SJS/TEN disease.(142)
20
SJS and TEN are relatively uncommon diseases, with incidences ranging from 2 to 5 cases per million per year.(143, 144) Although they are rare diseases, their importance lies in the high associated morbidity and mortality. Mortality rates of 3% and 25% to 40% have been reported for SJS and TEN respectively.(144, 145) Acute ocular complications are frequent (43%-81%) in more than a half of the patients hospitalized with diagnosis of SJS or TEN, with no difference in the rate of acute ocular complications between the groups.(146)
Even when SJS or TEN pathogenesis is thought to be an idiopathic immune reaction to medications (antibiotics, anticonvulsivants and non-steroideal antiinflammatory drugs), most cases are also associated to infectious diseases and a major percentage still remain undetermined.(147) There is evidence that supports that certain HLA alleles are associated with an increased risk or predisposition to severe skin or mucous reactions such as SJS. HLA-B*1502 and HLA-B*5801 have been identified as risk factors for developing SJS if exposed to carbamazepine and allopurinol respectively.(148) Table 7 summarizes some of the etiologies associated with SJS/TEN.
SJS and TEN are known to cause epidermal cell necrosis probably through a combination of mechanisms that include Fas-Fas ligand interactin, cytotoxic T-cells, tumor necrosis factor-alpha, and nitrous oxide syntase.(153, 154)
 
• Acute and Chronic Clinical Features
In the acute phase of the disease, that is the first two weeks of the disease, 15%-75% of the patients develop ocular lesions, manifested as bilateral conjunctivitis, mucous discharge and tarsal and forniceal conjunctival epithelial defects and ulcerations (Figure 15).(155) Approximately one fourth of these patients will develop more severe disease consisting on corneal epithelial defects and severe ocular surface inflammation.(146) If ulceration and inflammation is not managed during this stage, the healing process usually produces scarring of the conjunctiva. It is not clear if the ocular inflammatory process persists even after systemic inflammation is controlled and the patient is discharged from hospital.(155)
Chronic ocular sequelae, consequence of persistent inflammation, are frequent in up to one third of the patients with SJS.(156) Corneal severe scarring and ulceration or neovascularization are the most common form of long term complications, often leading to blindness.(157) In some patients, persistent inflammation may extend to reach the limbus, destroying the stem cell population and leading to a disease called stem cell deficiency. Limbal stem cell deficiency produces further conjunctivalization and fibrovascular scarring of the cornea, causing a more profound vision loss (Figure 16).(158) Conjuctival scarring will also produce fornix shortening, symblepharon and lid margin deformation. Lid margin or tarsus deformation can produce entropion, ectropion or eyelash alterations (distichiasis), fostering ocular surface microtrauma and exposition.(158) Extensive symblepharon will distort the ocular surface and the tear film distribution and produce ocular movement limitation and even induce an abnormal Bell's phenomenon.(158) In addition to this, scarring and keratinization of the main and accessory lacrimal ducts will enhance the dry eye syndrome (Figure 17).
Table 7   SJS/TEN reported possible etiologies (149; 150; 151; 152)
Table 7
ANTIBIOTICS
Penicillins, sulfas, ciprofloxacin
ANTICONVULSIVANTS
Phenytoin, carbamazepine, oxcarbazepine, valproic acid, lamotrigine, barbiturates
INFECTIOUS
Bacterial: Group A beta-hemolytic streptococci, diphtheria, brucelosis, lymphogranuloma venereum, mycobacteria, mycoplasma pneumonia, rickettsial infections, tularemia, typhoid
Viral: Herpes simplex virus (possibly; remains a debated issue), AIDS, coxsackie viral infections, influenza, hepatitis, mumps, Epstein-Barr
Fungus: coccidioidomycosis, dermatophytosis, and histoplasmosis
OTHER DRUG
Modafinil, allopurinol, mirtazapine, TNF-alpha antagonists (eg, infliximab, etanercept, adalimumab), cocaine
21
zoom view
Figure 15: Stevens-Johnson syndrome. Extensive conjuctival ulceration and scarring.
zoom view
Figure 16: Stevens-Johson syndrome. Conjuctival ulceration and scarring leading to extensive symblepharon formation.
zoom view
Figure 17: Stevens-Johnson syndrome. Severe corneal and conjunctival keratinization.
 
• Treatment Approaches
Treatment of SJS or TEN should start at bedside. Skin lesions, conjunctivitis and conjunctival ulcers should be intensively treated with lubricating ointment, topical antibiotics, cyclosporine and topical steroids as well as periodic symblepharon lysis using symblepharon rings.(159)
Several modalities of systemic treatment have been proposed for the treatment of SJS and TEN. If medication induced SJS is suspected, withdrawal of the offending drug should be the main concern. Plasmapheresis, immunosuppressive therapy and intravenous immunoglobulins (IVIg) have been used with variable results.(160) The role of systemic steroids is controversial, since high doses may wane inflammation but also can increase the risk of mortality and infection.(159,161) Intravenous IVIg have shown promising and encouraging results when given in high doses very early in the disease and for a short period.(160) Consensus on treatment has not been established, recent studies found no sufficient evidence of benefit for any specific treatment. Also neither treatment, IVIg nor systemic steroids, appear to have an effect on ocular outcomes.(162)
The use of amniotic membrane to cover the ocular surface entirely with or without the use of topical steroids during the acute phase of SJS or TEN has shown to be an effective treatment for conjunctival, eyelid and ocular surface inflammation; minimizing the cicatricial ocular sequelae and promoting the preservation of good visual acuity.(159, 163)
In chronic ocular disease induced by SJS, cumulative insults and cicatricial changes make ocular surgical reconstruction a major challenge. The need of allogenic stem cell transplant surgery in any of its variants is mandatory and in some cases the use of a keratoprosthesis is the only viable path to achieve some degree of visual function.(159)
 
Stem Cell Deficiency Disorders
 
 
• General Overlook
Corneal epithelium is a self-renewing tissue essential for the ocular biodefense system and together with a stable tear film, clear stroma and functional endothelium, indispensable for clear vision.(164) Complete turnover of epithelium occurs 22in approximately 5 to 7 days, eliminating superficial cells through a process of cell sloughing.(9) In order to have a constant renewal process, corneal epithelium must contain a viable stem cell pool.(165) A large body of evidence shows that these cells reside in the basal limbal region and are named limbal epithelial stem cells (LESC).(165) LESC cells are primitive slow cycle cells that share features of adult somatic stem cells including a small cell size, the lack of differentiation markers (such as cytokeratin), and a high nuclear to cytoplasm ratio.(166168) The corneoscleral limbus is the site of transition from the columnar epithelium of the conjunctiva, to the non keratinized, stratified squamous epithelium. The LESC are located at this anatomic site, specifically at the limbal palisades of Vogt where specific anatomical structures termed ‘limbal epithelial crypts’ (LEC) have been identified in the posterior end of the limbal palisades, showing features of a LESC niche.(12,13) LESC have been shown to express progenitor markers including, p63, ABCG2 and more recently N-cadherin; and to be deficient in differentiation keratin markers (CK19, CK3) expressed over the entire corneal epithelium, providing evidence that the basal limbal epithelium has the least differentiated cells of corneal epithelium.(165, 169)
Centripetal and circumferential migration occurs from the limbus and vertically from the basal layer forwards, following the “X,Y,Z hypothesis of corneal epithelial maintenance” proposed by Thoft and Friend.(170) One daughter LESC stays at the limbus pool of SC, meanwhile other continues to differentiation, acquiring features of corneal epithelium.(171) These cells known as “transient amplifying cells” migrate after a high but limited number of mitosis, becoming thereafter in “post mitotic cells” with no division potential.(171, 172)
Limbal stem cell deficiency (LSCD) can be primary, as a result of a deficient stromal microenvironment unable to support stem cell function: aniridia, congenital erythrokerato-dermia, keratitis associated with multiple endocrine deficiencies, neurotrophic keratopathy and chronic limbitis; or secondary (more common): associated to external injury and limbal stem cell destruction such as chemical or thermal injuries, Stevens-Johnson syndrome, ocular cicatricial pemphigoid, multiple surgeries, severe microbial infection or extended contact lens wear.(173175) Stem cell deficiency can be either partial or total, depending on the damage extent of the primary insult.(164) Also, in some patients LSCD can be subclinical at the time of the insult, and progress over time to a state of SC depletion where clinical LSCD may be manifest.(164)
In general, clinical presentation independently of the underlying etiology has consistent clinical features. Symptoms include photophobia, decreased vision, blepharospasm, tearing, foreign body sensation, recurrent episodes of pain (epithelial defects) and chronic red or irritated eye.(164) Slit lamp exam is characterized by irregular ocular surface and corneal epithelium, this latter can vary in thickness and transparency.(12) Chronic keratitis, corneal calcification and scarring along with fibrovascular pannus ingrowth are clinical hallmarks. Conjunctivalization of the corneal surface generally gives a granular or stippled late staining pattern since conjuctival epithelium is more permeable than corneal epithelium.(176) Conjunctivalized corneal epithelium is thinner, irregular and more susceptible to create recurrent epithelial erosions and to elicit neovascularization. Hence, persistent epithelial defects, melting, perforations and ulcers are frequent in LSCD.(176)
LSCD diagnosis is habitually made on basis of the clinical history and slit lamp findings. It can be histologically confirmed using impression cytology, which can detect goblet cells and conjuctival epithelium in the corneal surface.(169) Immunohisto-chemical tests to detect differentiation corneal markers such as cytokeratin 3, are negative in LSCD since these are absent in conjuctival epithelium.(176) Mucin cells have also been detected in the corneal surface using monoclonal antibodies.(176)
 
• Congenital Stem Cell Deficiency
Aniridia is the most representative cause of blindness associated with progressive ocular surface disease. This disease is caused by PAX6 heterozygosity, a condition that leads to variable degrees of bilateral iris hypoplasia, cataracts, optic nerve hypoplasia, glaucoma and corneal neovascularization.(177) The underlying abnormality process and precise etiology is poorly understood, but it is believed to be a consequence of congenital stem cell failure produced by LESC niche and microenvironment disturbances. A downregulation in PAX6 has been associated with abnormal epidermal differentiation of corneal epithelial cells, since it plays a key role for the expression of cytokeratins 3 and 12.(177,178) PAX6 is also related with the production of adhesion molecules as b-catenin and c-catenin. Deficient 23PAX6 mouses have shown spaces between epithelial cells and abnormal epithelial cells migration patterns during corneal healing.(165)
Aniridic keratopathy (AK) occurs in 90% of the patients with aniridia, it is one of the factors leading to severe and progressive vision loss in these patients.(179) LSCD usually begins to manifest in late childhood or during the teenage. Abnormal thickened and irregular epithelium is usually the first clinical finding, followed by superficial neovascularization that gradually progresses to fibrosis and stromal scarring (Figure 18).(180) Classic clinical findings of LSCD as corneal conjunctivalization, recurrent erosions and ulcers if untreated, lately produce corneal blindness.(179) Thus, the pathogenic mechanisms in AK are associated with a loss of cytokeratins and cell adhesion, resulting in an extremely fragile corneal surface that is prone to recurrent erosions and ulcerations.(180) Lopez-García et al, proposed a three stages classification of AK according to clinical features and symptoms (Table 8).
 
• Chemical Induced Damage
Ocular burns to the eyelids, conjunctiva, cornea and sclera whether from radiant energy or from chemical cause, can result in mild injury but can often cause devastating damage requiring prompt and adequate treatment to avoid ocular surface dysfunction and profound vision loss.(182) The degree of damage correlates with the kind of insulting agent, time of exposure and concentration and volume of solution in the case of chemical agents.(182) In general, chemical induced damage is more severe than radiant energy injuries, is more common in young males, and more than a half of the cases occur in the workplaces, particularly in industrial settings. Alkali injuries are twice as common as acid injuries, and are considered to be more severe.(183)
zoom view
Figure 18: Aniridia. Early aniridic keratopathy (AK), showing 360º conjunctivalization and corneal superficial neovascularization.
Alkaline injuries are usually due to ammonia and lye.(182) The substances are typically found on fertilizers and house hold cleaners, and have the characteristic to cause profound damage because of their lipid and water solubility. This solubility property and the ability to produce cell membrane saponification and form calcium soaps (specially calcium hydroxide), allow rapid penetration to the tissues, and can reach the anterior chamber in minutes.(184)
Table 8   Classification of Aniridic Keratopathy.
Table 8
Stages
Ulcer / Erosion
Vascular Pannus
Signs + Symptoms
1 Slight limbal insufficiency
Max two recurring erosions or ulcers within 6 months
Not exceeding 1 mm from the limbic arch
Small disorders in absorption of fluorescein; slight epiphora and photophobia
2 Moderate limbal insufficiency
More than three recurring erosions or ulcers within 6 months
Involves at least the peripheral half of the cornea ± subepithelial fibrosis
Permanent instability of the lacrimal film; constant red eye, epiphora and photophobia
3 Severe limbal insufficiency
Permanent signs of corneal erosion
Central cornea involved
Permanent instability of the lacrimal film; constant red eye, epiphora, photophobia and loss of vision
(Adapted from Lopez-Garcia JS, Garcia-Lozano I, Rivas L, et al. Congenital aniridia keratopathy treatment. Arch Soc Esp Oftalmol 2006; 81: 435–444.)
24
Further damage is induced by the release of hydroxyl ions that cause collagen fibers edema and later thickening and shortening.(185) Similar damage is caused on the conjunctiva, cornea, sclera and in the intraocular structures if anterior chamber is reached. Decreased levels of ascorbate, essential for collagen and glycosamynoglycans synthesis, are a hallmark since active transport from the ciliary body is compromised.(184)
Acid injuries are common since acid compounds are commonly found in house hold cleaners, rust remover and car batteries.(183) Sulfuric acid, found in car batteries is the most common cause of acid related injury (Figure 19). Hydrofluoric acid and hydrochloric acid are other acids that commonly cause chemical injury accident.(183) The former is used in house cleaning solutions or rust removers and it can penetrate tissues easily since its fluoride anion can dissolve cellular membranes, the latter is usually damaging to the eye except in high concentrations. Acids dissociate into hydrogen ions when forming a solution, causing cellular necrosis, protein denaturation and precipitation. Protein precipitation forms a barrier that further protects the eye from continuous damage. Glycosaminoglycans precipitation, epithelial cell coagulation and hydration of the collagen fibrils occur, affecting also de trabecular meshwork and producing high intraocular pressure (IOP). As with alkali injuries, ascorbate deficiency plays an important role in the pathogenesis of late ocular complications.(184)
zoom view
Figure 19: Sulfuric acid burn. Extensive necrosis of the corneal and conjuctival tissue. Perilimbal ischemia 360 degrees.
Corneal ulceration may be produced due to the combination of epithelial defects, inflammation, release of proteolytic enzymes (colagenase type I), tear deficiency and impaired collagen synthesis. Epithelial defects repairment requires from intact limbal stem cells, if LESC are not available due to extensive damage, conjunctiva must re-epithelize the corneal surface.(185)
Cellular injury to the conjunctiva, cornea, nerves and vessels are manifested as epithelial defects, conjunctival chemosis, perilimbal ischemia, inflammatory membranes in the anterior chamber, scleral thinning and necrosis, high intraocular pressure or hypotony (ciliary body shut down from damage), cataract formation and damage to the retina can be seen depending on the severity and extend of chemical burn (Figure 20).(185) Roper-Hall modified a classification proposed originally by Hughes to help guiding prognosis and treatment of chemical burns (Table 9).(186)
Initial treatment of chemical burns should be directed towards the elimination of the noxious agent and to change the pH to a physiologic level. Profuse irrigation with Ringer's lactate or isotonic balanced solution is mandatory, sometimes requiring volumes up to 20 liters to achieve pH normalization.(185) Once copious irrigation has achieved pH regularization, detailed ocular surface examination should be performed aided with the use of topical anesthetics. Removal of necrotic material and remaining solids that could act as reservoir for the chemical should be performed.(183)
zoom view
Figure 20: Severe alkali burn (Grade III Hughes-Roper-Hall Classification). Extensive chemosis, total loss of corneal epithelium, stromal haze and blurring iris details, ischemia in the inferior half of the limbus.
25
Table 9   Classification of severity of ocular surface burns by Hughes-Roper-Hall.
Table 9
Grade
Prognosis
Cornea
Conjunctiva/limbus
I
Good
Corneal epithelial damage
No limbal ischemia
II
Good
Corneal haze, iris details visible
<1/3 limbal ischemia
III
Guarded
Total epithelial loss, stromal haze, iris details obscured
1/3–1/2 limbal ischemia
IV
Poor
Cornea opaque, iris and pupil details obscured
>1/2 limbal ischemia
In this stage the treatment is focused on promoting the healing of corneal epithelium, treating the IOP if elevated, decrease inflammation and diminish the collagenolytic activity.(185)
The use of a bandage contact lens (BCL) and intense lubrication has proved to provide comfort to the patient. Antibiotic coverage is recommended if epithelial defect is present and a BCL is to be used.(182) Also, topical and oral ascorbate and topical citrate can promote epithelial healing and limit epithelial necrosis.(182) Topical steroids can be safely used the first 7 to 10 days after the event, since their effect on collagenase activity in this period is minimal.(187) After 10 days however, their use is associated with an increased risk of corneal melting and ulceration.(187) Topical medroxyprogesterone and oral tetracycline have shown to have anticollagenase effect and to inhibit neovascularization.(183) Therefore, the use of these latter is encouraged in the subacute phase of the treatment. Sodium citrate has demonstrated to decrease leukocyte phagocytosis, adherence, mediator release, and lysosomal enzyme release; its use as 10% solution has shown to be effective as prophylactic in the formation of corneal ulcers, decreasing their incidence from 80% (non treated eyes) to 4.6% in experimental alkali burns.(188)
After the acute and subacute phases of the treatment, the majority of these patients will develop a partial or total LESC depletion, since chronic inflammation will likely induce a sustained loss of these cells. The final treatment of these patients will consist on the replacement of LESC either from the fellow eye (autograft) when unilateral disease is present or from a relative or cadaveric donor (allograft).(182) If successful, limbal stem cell repopulation would increase the likelihood of an optic rehabilitation through a penetrating keratoplasty.
 
• Iatrogenic Limbal Stem Cell Deficiency
Medically or surgically induced damage to the LESC has been documented. Contact lens (CL) induced keratopathy is characterized by migration of conjunctival epithelium and goblet cell migration to the cornea.(189) It is thought to result as a consequence from chronic limbal SC damage and ischemia. In 1998, were identified a series of patients without knowing the secondary causes of LSCD sharing clinical features consisting on chronic, progressive epitheliopathy that began in the peripheral cornea and progressed centrally with neovascularization were identified.(190) These patients were similar to the patients in Tseng's “multiple surgeries or cryotherapies to the limbal region” group of LSCD.(191) Also, a common clinical history of ocular surgeries involving the limbus and more than 2 ocular surgeries was found on these patients.(190) Extracapsular and intracapsular cataract surgery involving 180º of the superior limbus was often associated with findings of partial LSCD, proposing direct trauma and limbal manipulation as a cause for SC damage.(190)
The chronic use of topical medications including pilocarpine, beta blockers, antibiotics, and steroids are proposed to play a role in the damage of LESC, since they are also toxic to the corneal epithelium.(164) Topical mitomycin C has been associated with direct toxicity to the LESC.(164)
 
• Treatment Options for LSCD
The ideal treatment for LSCD, no matter what etiology, is to restore the anatomical and physiological functions of the ocular surface. Initial treatment before reconstruction of the ocular surface includes 26the optimization of the surface microenvironment by using lubricants, bandage contact lens or tarsorraphy. Final rehabilitation will consists in a form of epithelial or limbal stem cell transplantation either from a donor (allograft) or from the fellow eye (autograft) in cases of unilateral disease. If this surgery is successful, regression of neovascularization, achievement of a smooth ocular surface, an improved vision and a higher likelihood of a functional keratoplasty may be reached. Keratoprosthesis is another treatment option when the likelihood of a successful limbal graft is low.
In 1996 a classification of limbal transplantation procedures was established to facilitate their understanding and to improve communication between surgeons.(192) This classification was based on the origin of the tissue (autograft / allograft) and further classifies the source of tissue in live tissue or cadaveric donor (Table 10).
Prior to the decision-making algorithm for surgery, a full assessment of the situation of systemic and ophthalmic patient should be done.(193)
  1. Lid position and alterations. Trichiasis, lagophthalmos, symblepharon.
  2. Presence of severe dry eye. Transplanting LESC is contraindicated in these patients because of the low graft survival rate with this situation.
    Table 10   Classification of epithelial transplantation procedures for severe ocular surface disease.
    Table 10
    Procedure
    Abbreviation
    Transplanted Tissue
    Conjunctival transplantation
    Conjunctival autograft
    CAU
    Conjunctiva
    Cadaveric conjunctival allograft
    c-CAL
    Conjunctiva
    Living related conjunctival allograft
    lr-CLAL
    Conjunctiva
    Living nonrelated conjunctival allograft
    lnr-CAL
    Conjunctiva
    Limbal transplantation
    Conjunctival limbal autograft
    CLAU
    Limbus/conjunctiva
    Cadaveric conjunctival limbal allograft
    c-CLAL
    Limbus/conjunctiva
    Living related conjunctival limbal allograft
    lr-CLAL
    Limbus/conjunctiva
    Living nonrelated conjunctival limbal allograft
    lnr-CLAL
    Limbus/conjunctiva
    Keratolimbal autograft
    KLAU
    Limbus/cornea
    Keratolimbal allograft
    KLAL
    Limbus/cornea
    Other mucosal transplantation
    Oral mucosa autograft
    OMAU
    Oral mucosa
    Nasal mucosa autograft
    NMAU
    Nasal mucosa
    Intestine mucosa autograft
    IMAU
    Intestinal mucosa
    Peritoneal mucosa autograft
    PMAU
    Peritoneum
    Ex vivo tissue engineered procedures
    Ex vivo cultivated conjunctival transplantation
    Ex vivo cultivated conjunctival autograft
    EVCAU
    Conjunctiva
    Ex vivo cultivated cadaveric conjunctival allograft
    EVc-CAL
    Conjunctiva
    Ex vivo cultivated living related conjunctival allograft
    EVlr-CAL
    Conjunctiva
    Ex vivo cultivated living non-related conjunctival allograft
    EVlnr-CAL
    Conjunctiva
    Ex vivo cultivated limbal transplantation
    Ex vivo cultivated cadaveric limbal allograft
    EVLAU
    Limbus/cornea
    Ex vivo cultivated cadaveric limbal allograft
    EVc-LAL
    Limbus/cornea
    Ex vivo cultivated living related limbal allograft
    EVlr-LAL
    Limbus/cornea
    Ex vivo cultivated living nonrelated limbal allograft
    EVlnr-LAL
    Limbus/cornea
    Other ex vivo cultivated mucosal transplantation
    Ex vivo cultivated oral mucosa autograft
    EVOMAU
    Oral mucosa
    (Adapted from Cornea, 3rd Edition By Jay H. Krachmer, MD, Mark J. Mannis. Based on the Cornea Society's International Committee for the Classification of Ocular Surface Rehabilitation Procedures, 2008.)
    27
  3. Presence and depth of corneal neovascularization.
  4. Estimation of intraocular pressure.
  5. Estimate the visual potential of the eye. Using B-mode ultrasound, visual evoked potentials or interferometry.
  6. Consider the risks of submitting the patient to a prolonged immunosupression. Undertake a comprehensive review of the overall health of the patient.
 
• Conjunctival - Limbal Autograft (CLAU)
This is a procedure in which limbal tissue is transplanted together with a conjunctival conveyor from a healthy eye, to the contralateral eye with LSCD. This procedure is ideal for patients with unilateral LSCD and has the advantage over allografts that it does not need of systemic immunosuppression.(192) It is of great importance to ensure that the healthy from which the graft will be taken does not have a condition that predisposes to LSCD. A potential risk involved in this procedure is to induce damage and limbal cell deficiency in the donor eye. Given this scenario, it is prudent for the surgeon to be conservative in patient selection and tissue dissection if the procedure is finally performed.(194)
Some authors suggest the use of amniotic membrane at the end procedure both to cover the epithelial defect and irregular corneal surface, and to protect conjuctival-limbal grafts by suturing the membrane with a 10-0 nylon suture at the edges of the retracted conjunctiva or using fibrin glue.(195196) Its use is considered a biologic therapeutic patch, promotes epithelial growth on the amniotic membrane over the cornea and may be withdrawn at 7-10 days if not lysed spontaneously.
 
• Living Related Conjunctival-Limbal Allograft (lr-CLAL)
In this procedure, the healthy conjunctiva from a living related of the patient is harvested and transplanted into the patient's eye with LSCD. The indications are similar to those of CLAU. The exception to this procedure is that the patient's contralateral eye usually has risk factors that may predispose LSCD (chronic use of medications, previous eye surgery, and ocular surface disease) or there is a bilateral LSCD.(192)
Unlike CLAU, in this procedure there is a risk of graft rejection. As in all allografts, the risk of rejection increases considerably if the receiving eye has active inflammation.(193) Thus, aggressive medical management of inflammation for a prolonged period is mandatory in order to obtain adequate immunosuppression and to maintain a good graft survival rate.(193)
Patient selection for this technique has to be focused on ruling out any systemic disease or condition (poorly controlled diabetes, kidney disease, myelodysplasia, liver disease) that may contraindicate immunosuppression. After this screening, patient's eye must be prepared to eliminate or lessen receptor factors that could decrease the rate of graft survival. That is, suppression of ocular surface inflammation with topical steroids, correction of eyelid abnormalities and management of dry eye (dry eye is a contraindication for this procedure).(197)
The postoperative management includes the use of topical steroids and antibiotics, and a systemic immunosuppression regimen that generally includes a T cell suppressor agent (tacrolimus or cyclosporine A) and an antimetabolite agent (mycophenolate mofetil or azathioprine).(198199)
The importance of the tissue source was emphasized by Reinhart et al.(200) Allograft is preferred, when possible, from a living related donor rather than from a cadaveric donor. They correlate the coincidences in HLA-I and HLA-II for patients with living related donor allografts compared with cadaveric allografts, and reported a 65% survival of grafts at one year in patients with 0-1 mismatches, 41% with 2 − 6 mismatches and 14% when there was no match in the HLA.
Recent series have also addressed the fact that autografts have the best long-term outcome followed by living related donor allografts, and that cadaver donor allografts have a comparatively poor outcome.(201)
 
• Keratolimbal Allograft (KLAL)
It is a procedure in which transplanted corneal and limbal tissue is cultivated from a cadaveric donor. The KLAL is designed to transfer a large number of LESC to the recipient eye, making it ideal for patients with total or complete deficiency of LESC. It is used in patients with bilateral total LSCD, in patients who are not willing to participate with related donors and that have risk factors for developing contralateral eye LSCD.(192)
28
KLAL is ideal for patients with pathology affecting the limbus and have little or no conjunctival involvement (the best example is aniridia).(192) This procedure can be also used in partial deficiency (making a partial or sectorial KLAL). Patients with ocular cicatricial pemphigoid, chemical burns or Stevens-Johnson syndrome with mild to moderate conjunctival involvement are usually candidates for this type of technique. As in the other grafts, it is extremely important to achieve ocular surface inflammation control prior the procedure to improve the chance of graft survival.(193)
As part of the preoperative evaluation, it is crucial to identify situations that could allocate KLAL rejection, infection or severe scarring. Correction of eyelid abnormalities and assessment of the severity of dry eye and / or keratinization of the ocular surface is a rule, being the latter two relative contraindications for the procedure. The use of autologous serum has been suggested in patients with dry eye and severe keratinization, yet the success is considerably lower in these scenarios.(202)
Postoperative inflammatory suppression has proved to be a favorable prognostic factor in patients who underwent KLAL. The use of amniotic membrane as a biological patch after KLAL has shown to suppress inflammation, facilitate re-epithelialization and reduce scarring in patients with preoperative severe inflammation (chemical burns).(203)
Again, as with all the allografts, the use of systemic immunosuppression is mandatory to ensure the viability of the graft.(199) Recent trends in keratolimbal allografts point towards the correction of ocular surface deficits combined with an immunosuppressive regimen (mycophenolate mofetil and tacrolimus) to further improve the long-term outcome of KLAL in eyes with total limbal stem cell deficiency.(204)
 
• Combined Procedures CLAL & KLAL
The combined procedure conjunctival limbal allograft and keratolimbal autograft is indicated in patients who have a total or subtotal loss LSCD and also have an extensive conjunctival involvement.(204) Candidates for this surgery are usually patients with advanced Stevens-Johnson syndrome, chemical burns and severe ocular cicatricial pemphigoid grade IV. Generally, this procedure is coupled with an extensive reconstruction of the ocular surface, including the oral mucosa for reconstruction of the fornix.(205)
 
• Simple Limbal Epithelial Transplantation (SLET)
Recently, Sangwan et al described a novel surgical technique of limbal transplantation in cases of unilateral and total limbal stem cell deficiency, which combines the benefits of existing techniques while apparently avoiding their difficulties.(206) Briefly in consist in taking a small 2 × 2 mm conjuctival-limbal autograft, which is later divided in eight to ten pieces. After recipient eye preparation, amniotic membrane is fixated over the recipient cornea using fibrin glue and the small pieces of graft are distributed evenly over the amniotic membrane. They achieved an avascular, epithelialised and stable ocular surface in all recipient eyes by 6 weeks, which were maintained for at least 9 months. Although long-term follow up results are still awaited; this seems to be a simple and effective technique for treating unilateral LSCD.
 
• Procedures Ex Vivo Tissue Engineering
The use of tissue obtained by bioengineering is the future of the rehabilitation of the ocular surface.(207) The possibility of obtaining large amounts of limbal stem cell tissue for transplant with a minimal amount of tissue for culture minimizes the risk of iatrogenic LSCD. The techniques consist basically of obtaining a tissue sample (allograft, but more importantly autograft) from a stem cell holder, and proliferate it in a substrate (i.e amniotic membrane) with a suitable microenvironment to later form a sheet of tissue and subsequently transplant it to the ocular surface.(207) Cultured oral mucosal epithelial stem cells have already been successfully used for the treatment of LSCE, in a procedure called COMET (cultivated oral mucosal epithelial transplantation).(208,209) Although promising for restoring the ocular surface, peripheral neovascularization is commonly seen in COMET.(208) Longer follow up is needed to assess the fate of this neovascularization and if anti angiogenic therapy would be beneficial in junction with COMET. Other sources of stem cells for culture and expansion are hair follicle stem cells, embryonic stem cells, conjunctival epithelial cells, dental pulp stem cells, umbilical cord lining stem cells, and bone marrow-derived mesenchymal stem cells.(210) The future suggests the possibility to differentiate autologous stem cells, thus avoiding the risk of rejection and the potential complications from systemic immunosuppression.
29
zoom view
Figure 21: Boston keratoprosthesis type 1.
zoom view
Figure 22: Retroprosthetic membrane in a patient with a Boston keratoprosthesis type 1.
zoom view
Figure 23: Tissue lysis and partial extrusion of a Boston KPro type 1.
 
• Keratoprosthesis
Boston keratoprosthesis (KPro) type I was approved in 1992 by the FDA for the management of severe corneal disease including basically repeat graft failure and limbal stem cell deficiency (primary or secondary); diseases that carry a poor prognosis with standard penetrating keratoplasty (PK) and ocular surface reconstruction (Figure 21).(211212)
Although far from perfect, recent modifications and improvements to the biomechanics of the KPro have contributed to improved outcomes; in such a way that recent studies compare the Boston KPro with PKP in terms of cost effectiveness and quality-adjusted life years.(213) The use of advanced materials and novel fixation methods for assembling them, have shown promise in the pursuit for a biointegratable KPro.(212) The prognosis of keratoprosthesis (KPro) procedures depends on the preoperative diagnosis, being graft failure and non cicatrizing disease the preoperative diagnosis with better prognosis, followed by ocular cicatricial pemphigoid, chemical burns and finally Stevens-Johnson syndrome has the more limited prognosis.(214) Still, the KPro arises many challenges that may restrict its success, such as severe glaucoma, retroprosthetic membranes, extrusion and lysis (Figures 22 and 23) and endophthalmitis.(211)
Recently, Sejpal et al reported the outcomes of Boston type 1 KPro in the management of LSCD.(215) They reported improvement in corrected distance visual acuity in the majority of patients with LSCD, with visual acuity of 20/50 or better in 69% of the patients after 3 years. The most common complication was persistent epithelial defect, and it was associated with stromal necrosis and low retention rates in eyes with immune-mediated LSCD. They recommended the use of Boston KPro type I in patients with bilateral LSCD non-immune mediated.
30
References
  1. Tsubota K, Tseng SCG, Nordlund ML. Anatomy and Physiology of the Ocular Surface. Ocular Surface Disease - Medical and Surgical Management. Springer;  New York:  2002.
  1. Kersten R, et al. The Foundation of the American Academy of Ophthalmology. Orbit, Eyelids and Lacrimal System. In: al KHe, ed. Basic and Clinical Science Course. San Francisco; 2008.
  1. Tiffany JM. The role of meibomian secretion in the tears. Trans Ophthalmol Soc U K. 1985;4 (104): 396–401.
  1. M Mannis, E Holland J Krachmer. Cornea. Mosby;  St Louis:  2011.
  1. Lowry JC, Bartley GB. Complications of blepharoplasty. Surg Ophthalmol. 1994;38(4):327–50.
  1. Bashour M, Harvey J. Causes of involutional ectropion and entropion—age-related tarsal changes are the key. Ophthal Plast Reconstr Surg. 2000;16(2):131–41.
  1. Nelson J, Cameron J. The Conjunctiva. Cornea. Vol Vol 1. 3rd ed. Mosby;  St. Louis:  2011.
  1. Wei ZG, Cotsarelis G, Sun TT, Lavker RM. Label-retaining cells are preferentially located in fornical epithelium: implications on conjunctival epithelial homeostasis. Invest Ophthalmol Vis Sci. 1995;36(1):236–46.
  1. Nishida T, Saika S. Cornea and Sclera : Anatomy and Physiology. Cornea. Vol Vol. 1. 3rd ed. Mosby;  St. Louis:  2011.
  1. Barry PA, Petroll WM, Andrews PM, Cavanagh HD, Jester JV. The spatial organization of corneal endothelial cytoskeletal proteins and their relationship to the apical junctional complex. Invest Ophthalmol Vis Sci. 1995;36((6)):1115–24.
  1. Nichols B DCTB. Surface features of the conjunctiva and cornea. Invest Ophthalmol Vis Sci. 1983;24(5):570–6.
  1. Dua HS, Forrester JV. The corneoscleral limbus in human corneal epithelial wound healing. Am J Ophthalmol. 1990;110:646–56.
  1. Dua HS, Shanmuganathan VA, Powell-Richards AO, Tighe PJ, Joseph A. Limbal epithelial crypts: a novel anatomical structure and a putative limbal stem cell niche. Br J Ophthalmol. 2005;89:529–32.
  1. Grueterich M, Espana EM, Tseng SCG. Ex Vivo Expansion of Limbal Epithelial Stem Cells: Amniotic Membrane Serving as a Stem Cell Niche. Surv Ophthalmol. 2003;48:631–646.
  1. Puangsricharern V, Tseng SCG. Cytologic evidence of corneal diseases with limbal stem cell deficiency. Ophthalmology. 1995;102:1476–85.
  1. Patel S, Blades KJ. The dry eye - a practical approach. London: Elsevier; 2003.
  1. Goto E, Ishida R, Kaido M. Optical aberrations and visual disturbances with dry eye. Ocul Surf. 2006;4(4):207–213.
  1. Korb DR, Craig J, Doughty M The tear film. Butterworth-Heinemann / Elsevier;  London:  2002.
  1. Gipson IK, Tisdale AS. Visualization of conjunctival goblet cell actin cytoskeleton and mucin content in tissue whole mounts. Exp. Eye Res. 1997;65:407–415.
  1. King-Smith PE, Fink BA, Fogt N, et al. The thickness of the human precorneal tear film: evidence from reflection spectra. Invest Ophthalmol Vis Sci. 2000;41:3348–3359.
  1. Lemp MA, Beuerman RW. The Tear Film. Cornea. Vol Vol. 1. 3rd ed. Mosby;  St. Loius:  2011.
  1. Dilly PN. Structure and function of the tear film. Adv Exp Med Biol. 1994;350:239–247.
  1. Baier G, Wollensak G, Mur E, et al. Analysis of human tear proteins by different high performance liquid chromatographic techniques. J Chromatogr. 1990;525:319–328.
  1. Bron AJ, Tiffany JM. The meibomian glands and tear film lipids; structure, function and contro. Adv Exp Med Biol. 1998;438:281–295.
  1. Prydal JI, Artal P, Woon H, et al. Study of human tear film thickness and structure using laser interferometry. Invest Ophthalmol Vis Sci. 1992;33:2006–11.
  1. Lemp MA, Nichols KK. Blepharitis in the United States 2009: a survey-based perspective on prevalence and treatment. Ocul Surf. 2009;7(suppl):S1–14.
  1. McCulley JP, Shine WE. Changing Concepts in the Diagnosis and Management of Blepharitis. Cornea. 2000;19(5):650–658.
  1. Nelson JD, Shimazaki J, Benitez-del-Castillo JM, et al. The International Workshop on Meibomian Gland Dysfunction: Report of the Definition and Classification Subcommittee. Invest Ophthalmol Vis Sci. 2011;52(4):1931–1937.
  1. Foulks GN, Bron AJ. Meibomian gland dysfunction: a clinical scheme for description, diagnosis, classification, and grading. Ocul Surf. 2003;1:107–126.
  1. Bron AJ, Tiffany JM. The contribution of meibomian disease to dry eye. Ocul Surf. 2004;2:149–164.
  1. Driver PJ, Lemp MA. Meibomian gland dysfunction. Surv Ophthalmol. 1996;40:343–67.
  1. Foulks GN. Blepharitis: Lid Margin Disease and the Ocular Surface. Ocular Surface Disease. New York: Springer; 2002.
  1. Friedlaender MH, Protzko E. Clinical development of 1% azithromycin in DuraSite, a topical azalide anti-infective for ocular surface therapy. Clin Ophthalmol. 2007;1(1):3–10.
  1. Fadlallah A, Rami HE, Fahd D, et al. Azithromycin 1.5% ophthalmic solution: efficacy and treatment modalities in chronic blepharitis. Arq Bras Oftalmol. 2012;75(3):178–82.
  1. Dougherty JM, McCulley JP, Silvany RE, Meyer DR. The role of tetracycline in chronic blepharitis: inhibition of lipase production in Staphylococci. Invest Ophthalmol Vis Sci. 1991;32:2970–5.
  1. Ta CN, Shine WE, McCulley JP. Effects of Minocycline on the Ocular Flora of Patients with Acne Rosacea or Seborrheic Blepharitis. Cornea. 2003;22(6):545–548.
  1. Brown NA, Bron AJ, Harding JJ, et al. Nutritional supplements and the eye. Eye. 1998;12:127–133.
  1. Wilkin JK. Rosacea. Arch Dermatol. 1994;130: 359.
  1. Wise G. Ocular rosacea. Am J Ophthalmol. 1943;26:591–609.
  1. Browning D, Browning D, Proia A. Ocular rosacea. Surv Ophthalmol. 1986;31:145–158.
  1. Tanzi E, Weinberg J. The ocular manifestations of rosacea. Cutis. 2001;68:112–114.
  1. Nazir SA, Murphy S, et al. Ocular Rosacea in Childhood. Am J Ophthalmol. 2004;137.
  1. Hoang-Xuan T, et al. Ocular rosacea. Ophthalmology. 1990;97: 1468.
  1. Bernstein JE, Soltani K. Alcohol-induced rosacea flushing blocked by naloxone. BrJ Dermatol. 1982;107:59–62.
  1. Li J, O'Reilly N, Sheha H, Katz R, Raju VK, Kavanagh K, Tseng SC. Correlation between ocular Demodex infestation and serum immunoreactivity to Bacillus proteins in patients with Facial rosacea. Ophthalmology. 2010;117(5):870–877.
  1. Starr PAJ, McDonald A. Oculocutaneous aspects of rosacea. Proc R Soc Med. 1969;62(9).
  1. Durson D, Piniella AM, Pflugfelder SC. Pseudokeratoconus caused by rosacea. Cornea. 2001;20: 668.
  1. Kligman A. Ocular rosacea. Arch Dermatol. 1997;133:89–90.
  1. Knox CM, Smolin G. Rosacea. Ophthalmol Clin. 1997;37:29–40.
  1. Çetinkaya AG, Akova YA. Pediatric Ocular Acne Rosacea: LongTerm Treatment With Systemic Antibiotics. Am J Ophthalmol;. 2006;142:816–821.
  1. Jones SM, Weinstein JM. Visual Outcome and Corneal Changes in Children with Chronic Blepharokeratoconjunctivitis. Ophthalmology. 2007;114:2271–2280.
  1. Brewitt H, Sistani F. Dry eye disease: the scale of the problem. Surv Ophthalmol. 2001;45:199–202.
  1. J Schein OD, Munoz B, Tielsch M, et al. Prevalence of dry eye among the elderly. Am J Ophthalmol. 1997;124:723–728.
  1. Schaumberg DA, Sullivan DA, Buring JE, et al. Prevalence of dry eye syndrome among US women. Am J Ophthalmol. 2003;326:136:318.

  1. 31 Lemp MA. Epidemiology and classification of dry eye. Adv Exp Med Biol. 1998;438:791–803.
  1. Schiffman RM, Walt JG, Jacobsen G, et al. Utility assessment among patients with dry eye disease. Ophthalmology. 2003;110:1412–9.
  1. Workshop Epidemiology Subcommittee of the International Dry Eye. The epidemiology of dry eye disease: report of the Epidemiology Subcommittee of the International Dry Eye Workshop. Ocul Surf. 2007;5: 99.
  1. de Paiva CS, Pflugfelder SC. Diagnostic approaches to lacrimal keratoconjunctivitis. Dry Eye and Ocular Surface Disorders. Marcel Dekker;  New York:  2004.
  1. Goto E, Yagi Y, Matsumoto Y, et al. Impaired functional visual acuity ofdry eye patients. Am J Ophthalmol. 2002;133:181–186.
  1. Stern ME, Beuerman RW, Fox RI, et al. The pathology of dry eye: the interaction between the ocular surface and lacrimal glands. Cornea. 1998;17:584–9.
  1. Bacman S, Berra A, Sterin-Borda L, Borda E. Muscarinic acetylcholine receptor antibodies as a new marker of dry eye Sjogren syndrome. Invest Ophthalmol Vis Sci. 2001;42:321–7.
  1. Solomon A, Dursun D, Liu Z, et al. Pro-and anti-inflammatory forms of interleukin-1 in the tear fluid and conjunctiva of patients with dry-eye disease. Invest Ophthalmol Vis Sci. 2001;42:2283–92.
  1. Pflugfelder SC. Antiinflammatory therapy for dry eye. Am J Ophthalmol. 2004;137: 338.
  1. Workshop Lemp MA (Chair), Definition and Classification Subcommittee of the International Dry Eye. The definition and classification of dry eye disease: report of the Definition and Classification Subcommittee of the International Dry Eye Workshop. Ocul Surf. 2007;5:75–92.
  1. Wilson SE, Stulting RD. Agreement of Physician Treatment Practices With the International Task Force Guidelines for Diagnosis and Treatment of the Dry Eye Disease. Cornea. 2007;26:284–289.
  1. Pflugfelder SC, Solomon A. Dry Eye. Ocular Surface Disease, Medical and Surgical Management. Springer;  New York:  2002.
  1. Pflugfelder SC, Tseng SC, Sanabria O, et al. Evaluation of subjective assessments and objective diagnostic tests for diagnosing tear-film disorders known to cause ocular irritation. Cornea. 1998;17:38–56.
  1. Afonso AA, Monroy D, Stern ME, Tseng SCG, Tseng SCG, Pflugfelder SC. Correlation of tear fluorescein clearance and Schirmer test scores with ocular irritation symptoms. Ophthalmology. 1999;106:803–810.
  1. Van Bijsterveld OP. Diagnostic tests in sicca syndrome. Arch Ophthalmol. 1969;82:10–14.
  1. Jones LT. The lacrimal secretory system and its treatment. Am J Ophthalmol. 1966;62:47–60.
  1. Whitcher JP, Shiboski CH, Shiboski SC, et al. A simplified quantitative method for assessing keratoconjunctivitis sicca from the Sjögren'sSyndrome International Registry. Am J Ophthalmol. 2010;149(3):405–15.
  1. Whichter PJ, Shiboski CH, Shiboski SC, et al. A Simplified Quantitative Method for Assessing Keratoconjunctivitis Sicca From the Sjögren Syndrome International Registry. Am J Ophthalmol. 2010;149: 405–415.
  1. Behrens A, Doyle JJ, Stern L, et al. Dysfunctional tear syndrome: a Delphi approach to treatment recommendations. Cornea. 2006;25:900–907.
  1. Geerling G, MacLennan S, Hartwig D. Autologous serum eye drops for ocular surface disorders. Br J Ophthalmol. 2004;88:1467–1474.
  1. Lee GA, Hirst LW. Ocular surface squamous neoplasia. Surv Ophthalmol. 1995;39:429–450.
  1. Basti S, Macsai MS. Ocular surface squamous neoplasia: a review. Cornea. 2003;22:687–704.
  1. Shields JA, Shields CL, Gunduz K, et al. The 1998 Pan American Lecture. Intraocular invasion of conjunctival squamous cell carcinoma in five patients. Ophthal Plast Reconstr Surg. 1999;15:153–160.
  1. Templeton AC. Tumors of the eye and adnexa in Africans in Uganda. Cancer. 1967;20:1689–1698.
  1. Sun EC, Fears TR, Goedert JJ. Epidemiology of squamous cell conjunctival cancer. Cancer Epidemiol Biomarkers Prev. 1997;6:73–77.
  1. Erie JC, Campbell RJ, Leisgang J. Conjunctival and corneal intraepithelial and invasive neoplasia. Ophthalmology. 1986;93:176–183.
  1. Pizzarello LD, Jakobiec FA. Bowen's disease of the conjunctiva: a misnomer. Ocular and Adnexal Tumors. Birmingham, AL: Aesculapius; 1978.
  1. Ni C, Searl SS, Kriegstein HJ, et al. Epibulbar carcinoma. Int Ophthalmol Clin. 1982;22:1–33.
  1. Newton R. A review of the etiology of squamous cell carcinoma of the conjunctiva. Br J Cancer. 1996;74:1511–1513.
  1. Clear AS, Chirambo MC, Hutt MSR. Solar keratosis, pterygium and squamous cell carcinoma of the conjunctiva in Malawi. Br J Ophthalmol. 1979;63:102–109.
  1. Trosko JE, Krause D, Isoun M. Sunlight-induced pyrimidine dimers in human cells in vitro. Nature. 1970;228:358–359.
  1. Brash DE, Rudolph JA, Simon JA, et al. A role for sunlight in skin cancer: UV-induced p 53 mutations in squamous cell carcinoma. Proc Natl Adad Sci USA. 1991;88:10124–10128.
  1. Vogelstein B, Kinzler KW. Carcinogens leave fingerprints. Nature. 1992;355:209–210.
  1. Scott IU, Karp CL, Nuovo GJ. Human papillomavirus 16 and 18 expression in conjunctival intraepithelial neoplasia. Ophthalmology. 2002;109:542–547.
  1. Kao AA, Galor A, Karp CL. Clinicopathologic Correlation of Ocular Surface Squamous Neoplasms at Bascom Palmer Eye Institute: 2001 to 2010. Ophthalmology. 2012;article in press.
  1. Sanders N, Bedotto C. Recurrent carcinoma in situ of the conjunctiva and cornea (Bowen's disease). Am J Ophthalmol. 1972;74:688–93.
  1. Blodi FC. Squamous cell carcinoma of the conjunctiva. Doc Ophthalmol. 1973;34:93–108.
  1. Cameron JA, Hidayat AA. Squamous cell carcinoma of the cornea. Am J Ophthalmol. 1991;111:571–574.
  1. Hamam R, Bhat P, Foster CS. Conjunctival/corneal intraepithelial neoplasia. Int Ophthalmol Clin. 2009;49:63–70.
  1. Tole DM, McKelvie PA, Daniell M. Reliability of impression cytology for the diagnosis of ocular surface squamous neoplasia Reliability of impressioncytology for the diagnosis of ocular surface squamous neoplasia employing the Biopore membrane. Br J Ophthalmol. 2001;85:154–8.
  1. Mader TH, Stulting RD. A new method of obtaining cells from the cornea and conjunctiva for cytologic study (letter). Arch Ophthalmol. 1990; 108: 639.
  1. Thiel MA, Bossart W, Bernauer W. Improved impression cytology techniques for the immunopathological diagnosis of superficial viral infections. Br J Ophthalmol. 1997;81:984–988.
  1. Nolan GR, Hirst LW, Bancroft BJ. The cytomorphology of ocular surface squamous neoplasia by using impression cytology. Cancer. 2001;93:60–67.
  1. Kieval JZ, Karp CL, Shousha MA. Ultra-High Resolution Optical Coherence Tomography for Differentiation of Ocular Surface Squamous Neoplasia and Pterygia. Ophthalmology. 2012;119:481–486.
  1. Shields JA, Shields CL, De Potter P. Surgical management of conjunctival tumors: the 1994 Lynn B. McMahan Lecture. Arch Ophthalmol. 1997;115:808–15.
  1. Tunc M, Char DH, Crawford B, Miller T. Intraepithelial and invasive squamous cell carcinoma of the conjunctiva: analysis of 60 cases. Br J Ophthalmol. 1999;83: Br J Ophthalmol-103.
  1. Peksayar G, Altan-Yaycioglu R, Onal S. Excision and cryosurgery in the treatment of conjunctival malignant epithelial tumours. Eye. 2003;17:228–32.
  1. Sturges A, Butt AL, Lai JE, Chodosh J. Topical interferon or surgical excision for the management of primary ocular surface squamous neoplasia. Ophthalmology. 2008;115:1297–302.

  1. 32 Birkholz ES, Goins KM, Sutphin JE. Treatment of Ocular Surface Squamous Cell Intraepithelial Neoplasia With and Without Mitomycin C. Cornea. 2011;30:37–41.
  1. Sepulveda R, Pe'er J, Midena E, et al. Topical chemotherapy for ocular surface squamous neoplasia: current status. Br J Ophthalmol. 2010;94:532–535.
  1. Kim HJ, Shields CL, Shah SU, et al. Giant Ocular Surface Squamous Neoplasia Managed with Interferon Alpha-2b as Immunotherapy or Immunoreduction. Ophthalmology. 2012;119:938–944.
  1. Yeatts RP, Engelbrecht NE, Curry CD, et al. 5-Fluorouracil for the treatment of intraepithelial neoplasia of the conjunctiva and cornea. Ophthalmology. 2000;107:2190–5.
  1. Vann RR, Karp CL. Perilesional and topical interferon alfa-2b for conjunctival and corneal neoplasia. Ophthalmology. 1999;106:91–7.
  1. Singh AD, Jacques R, Rundle PA, et al. Neoadjuvant topical mitomycin C chemotherapy for conjunctival and corneal intraepithelial neoplasia. Eye. 2006;20:1092–4.
  1. Parrozzani R, Lazzarini D, Alemany-Rubio E, Urban F, Midena E. Topical 1% 5-fluorouracil in ocular surface squamous neoplasia: a long-term safety study. Br J Ophthalmol. 2011;95((3)):355–9.
  1. Yeatts RP, Engelbrecht NE, Curry CD, et al. 5-Fluorouracil for the treatment of intraepithelial neoplasia of the conjunctiva and cornea. Ophthalmology. 2000;107:2190–5.
  1. Poothullil AM, Colby KA. Topical Medical Therapies for Ocular Surface Tumors. Semin Ophthalmol. 2006;21:161–169.
  1. Prabhasawat P, Tarinvorakup P, Tesavibul N, et al. Topical 0.002% mitomycin C for the treatment of conjunctival-corneal intraepithelial neoplasia and squamous cell carcinoma. Cornea. 2005;24:443–8.
  1. Frucht-Pery J, Sugar J, Baum J, Sutphin JE, Pe'er J, Savir H, et al. Mitomycin C treatment for conjunctival-corneal intraepithelial neoplasia: a multicenter experience. Ophthalmology. 1997;104(12): 2085–93.
  1. Boehm MD, Huang AJ. Treatment of recurrent corneal and conjunctival intraepithelial neoplasia with topical interferon alfa 2b. Ophthalmology. 2004;111:1755–61.
  1. Schechter BA, Koreishi AF, Karp CL, et al. Long-term follow-up of conjunctival and corneal intraepithelial neoplasia treated with topical interferon alfa-2b. Ophthalmology. 2008;115:129–133.
  1. Galor A, Karp CL, Chhabra S, Barnes S, Alfonso EC. Topical interferon alpha 2b eye-drops for treatment of ocular surface squamous neoplasia: a dose comparison study. Br J Ophthalmol. 2010;94:551–554.
  1. Shields CL, Shields JA. Tumors of the conjunctiva and cornea. Surv Ophthalmol. 2004;49:3–24.
  1. Foster CS. Cicatricial pemphigoid. Trans Am Ophthalmol Soc. 1986;84:527–623.
  1. Kirzhner M, Jakobiec FA. Ocular Cicatricial Pemphigoid: A Review of Clinical Features, Immunopathology, Differential Diagnosis, and Current Management. Semin Ophthalmol. 2011;26((4-5)):270–277.
  1. Chan LS. Mucous membrane pemphigoid. Clin Dermatol. 2001;19:703–11.
  1. Foster CS, Sainz de la Maza M. Ocular cicatricial pemphigoid review. Curr Opin Allergy Clin Immunol. 2004;4:435–9.
  1. Thorne JE, Anhalt GJ, Jabs DA. Mucous membrane pemphigoid and pseudopemphigoid. Ophthalmology. 2004;111:45–52.
  1. Ahmed M, Zein G, Khawaja F, Foster CS. Ocular cicatricial pemphigoid: pathogenesis, diagnosis and treatment. Prog Retin Eye Res. 2004;23:579.92.
  1. Hingorani M, Lightman S. Ocular cicatricial pemphigoid. Curr Opin Allergy Clin Immunol. 2006;6:373–8.
  1. Foster CS. Cicatricial pemphigoid. Cornea: Fundamentals, Diagnosis, and Management. Vol Vol 1.3rd ed. Mosby Elsevier Inc.  Philadelphia:  2011.
  1. Tyagi S, Bhol K, Natarajan K, et al. Ocular cicatricial pemphigoid antigens: Partial sequence and characterization. Proc Nat Acad Sci USA. 1996;93:14714–14719.
  1. Mondino BJ, Brown SI. Ocular cicatricial pemphigoid. Ophthalmology. 1981;88:95–100.
  1. Foster CS, Wilson LA, Ekins MB. Immunosuppressive therapy for progressive ocular cicatricial pemphigoid. Ophthalmology. 1982;89:340–353.
  1. Chan LS, Ahmed AR, Anhalt GJ, et al. The first international consensus on mucous membrane pemphigoid: definition, diagnostic criteria, pathogenic factors, medical treatment, and prognostic indicators. Arch Dermatol. 2002;138:370–9.
  1. Thorne JE AGJDea. Role of electron microscopy in the diagnosis of ocular mucous membrane pemphigoid. Ophthalmology. 2006;113:1651–6.
  1. Thorne JE, Anhalt GJ, Jabs DA, et al. Cicatricial pemphigoid serial titres of circulating IgG and IgA antibasement membrane antibodies correlate with disease activity. Br J Dermatol. 1999;140:645–50.
  1. Thorne JE, Woreta FA, Jabs DA, et al. Treatment of Ocular Mucous Membrane Pemphigoid with Immunosuppressive Drug Therapy. Ophthalmology. 2008;115:2146–2152.
  1. McCluskey P, Chang JH, Singh R, et al. Methotrexate Therapy for Ocular Cicatricial Pemphigoid. Ophthalmology. 2004;111:796–801.
  1. Letko E, Miserocchi E, Daoud YJ, et al. A nonrandomized comparison of the clinical outcome of ocular involvement in patients with mucous membrane (cicatricial) pemphigoid between conventional immunosuppressive and intravenous immunoglobulin therapies. Clin Immunol. 2004;111:303–10.
  1. Doan S, Lerouic JF, Robin H. Treatment of Ocular Cicatricial Pemphigoid with Sulfasalazine. Ophthalmology. 2001;108:1565–1568.
  1. Doycheva D, Deuter C, Blumenstock G. Long-term Results of Therapy with Mycophenolate Mofetil in Ocular Mucous Membrane Pemphigoid. (6), 2011, Ocular Immunology & Inflammation, 2001;19:31–438.
  1. Foster CS, Chang PY, Ahmed AR. Combination of rituximab and intravenous immunoglobulin for recalcitrant ocular cicatricial pemphigoid: A preliminary report. Ophthalmol 2010;17: 861–9.
  1. Gürcan HM, Keskin DB, Stern JN, et al. A review of the current use of rituximab in autoimmune diseases. Int Immunopharmacol 2009;9:10–25.
  1. Roujeau JC, Stern RS. Severe adverse cutaneous reactions to drugs. N Engl J Med 1994;331:1272–1285.
  1. Gueudry J, Roujeau JC, Binaghi M, Soubrane G, Muraine M. Risk factors for the development of ocular complications of Stevens-Johnson syndrome and toxic epidermal necrolysis. Arch Dermatol 209;145:157–162.
  1. Wetter DA, Camilleri MJ. Clinical, Etiologic, and Histopathologic Features of Stevens-Johnson Syndrome During an 8-Year Period at Mayo Clinic. Mayo Clin Proc 2010;85:131–138.
  1. Bastuji-Garin S, Rzany B, Stern RS, Shear NH, Naldi L, Roujeau JC. Clinical classification of cases of toxic epidermal necrolysis, Stevens-Johnson syndrome, and erythema multiforme. Arch Dermatol 1993:129:92–96.
  1. Paquet P, Pierard GE, Quatresooz P. Novel treatments for drug-induced toxic epidermal necrolysis (Lyell's syndrome). Int Arch Allergy Immunol 2005;136:205–16.
  1. Mockenhaupt M, Viboud C, Dunant A, et al. Stevens-Johnson syndrome and toxic epidermal necrolysis: assessment of medication risks with emphasis on recently marketed drugs: the EuroSCAR-study. J Invest Dermatol 2008;128:5–44.
  1. Yamane Y, Aihara M, Ikezawa Z. Analysis of Stevens-Johnson syndrome and toxic epidermal necrolysis in Japan from 2000 to 2006. Al-lergol Int 2007;6:419–425.
  1. Power WJ, Ghoraishi M, Merayo-Lloves J, et al.Analysis of the acute ophthalmic manifestations of the Erythema multiforme/Stevens-Johnson syndrome/toxic epidermal necrolysis disease spectrum. Ophthalmology 1995;102:1669–76.

  1. 33 Shammas MC, Lai EC, Sarkar JS, Yang J, Starr CE, Sippel KC. Management of acute Stevens-Johnson syndrome and toxic epidermal necrolysis utilizing amniotic membrane and topical corticosteroids. Am J Ophthalmol 2010;149:203–213.
  1. Fernando SL, Broadfoot AJ. Prevention of severe cutaneous adverse drug reactions: the emerging value of pharmacogenetic screening. CMAJ 2010;182:476–80.
  1. Hillebrand-Haverkort ME, Budding AE, bij de Vaate LA, van Agtmael MA. Mycoplasma pneumoniae infection with incomplete Stevens-Johnson syndrome. Lancet Infect Dis 2008; 8,:586–7.
  1. Mockenhaupt M, Messenheimer J, Tennis P, Schlingmann J. Risk of Stevens-Johnson syndrome and toxic epidermal necrolysis in new users of antiepileptics. Neurology 2005;64:1134–8.
  1. Halevy S, Ghislain PD, Mockenhaupt M, et al. Allopurinol is the most common cause of Stevens-Johnson syndrome and toxic epidermal necrolysis in Europe and Israel. (1), , J Am Acad Dermatol 2008;58:25–32.
  1. Stevens-Johnson syndrome complicating adalimumab therapy in Crohn's disease. Salama M, Lawrance IC. (35), 2009, World J Gastroenterol, Vol. 15, págs. 4449–52.
  1. Nassif A, Bensussan A, Dorothee G, et al. Drug specific cytotoxic T-cells in the skin lesions of a patient with toxic epidermal necrolysis. J Invest Dermatol 2002;18:28—33.
  1. Khalili B, Bahna SL. Pathogenesis and recent therapeutic trends in Stevens-Johnson syndrome and toxic epidermal necrolysis. (3), , Ann Allergy Asthma Immunol 2006;7:272–80.
  1. Shay ES, Kheirkhah A, Liang L. Amniotic Membrane Transplantation as a New Therapy for the Acute Ocular Manifestations of Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis. Surv Ophthalmol 2009;54:686–696.
  1. Arstikaitis MJ. Ocular aftermath of Stevens—Johnson syndrome. Arch Ophthalmol, 1973;90:376–9.
  1. Morales ME, Purdue GF, Verity SM, et al. Ophthalmic Manifestations of Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis and Relation to SCORTEN. Am J Ophthalmol 2010;150:505–510.
  1. Chang YS, Huang FC, Tseng SH, Hsu CK, Ho CL, Sheu HM. Erythema multiforme, Stevens-Johnson syndrome, and toxic epidermal necrolysis: acute ocular manifestations, causes, and management. Cornea 2007;26:123–129.
  1. Tseng SC. Acute management of Stevens-Johnson syndrome and toxic epidermal necrolysis to minimize ocular sequelae. Am J Ophthalmol 2009;147:949–51.
  1. Sotozono C, Ueta M, Koizumi N, et al. Diagnosis and treatment of Stevens-Johnson syndrome and toxic epidermal necrolysis with ocular complications. Ophthalmology 2009;116:685–90.
  1. Araki Y, Sotozono C, Inatomi T, et al. Successful treatment of Stevens-Johnson syndrome with steroid pulse therapy at disease onset. Am JOphthalmol 2009; 147:1004–11.
  1. Schneck J, Fagot JP, Sekula P, et al. Effects of treatments on the mortality of Stevens-Johnson syndrome and toxic epidermal necrolysis: A retrospective study on patients included in the prospective EuroSCAR Study. J Am Acad Dermatol 2008;58:33–40.
  1. Gregory DG. Treatment of Acute Stevens–Johnson Syndrome and Toxic Epidermal Necrolysis Using Amniotic Membrane: A Review of 10 Consecutive Cases. Ophthalmology 2008;118:908–914.
  1. Dua HS, Saini JS, Azuara-Blanco A, Gupta P. Limbal stem cell deficiency : Concept, aetiology, clinical presentation, diagnosis and management. Indian J Ophthalmol 2000;48:83–92.
  1. Ecker GA, Daniels JT. Secker GA, Daniels JT. Corneal Epithelial Stem Cells: Deficiency and Regulation. Stem Cell Rev 2008: 4:159–168.
  1. Romano AC, Espana EM, Yoo SH, et al. Different cell sized in human limbal and central corneal basal epithelia measured by confocal microscopy and flow cytometry., Invest Ophthalmol Vis Sci 2003;44:5125–5129.
  1. Schermer A, Galvin S, Sun TT. Differentiation related expression of a major 64K corneal keratin in vivo and in culture suggests limbal location of corneal epithelial stem cells. J Cell Biol 1986;103:49–62.
  1. Kurpakus MA. Stock EL, Jones JC. Expression of the 55-kD/64-kD corneal keratins in ocular surface epithelium. Invest Ophthalmol Vis Sci 1990;31:448–456.
  1. Kenyon KR, Bulusoglu G, Ziske JD. Clinical pathologic correlations of limbal autograft transplantation. Am J Ophthalmol 1990;31:1–12.
  1. Thoft RA, Friend J. The X, Y, Z hypothesis of corneal epithelial maintenance., Invest Ophthalmol Vis Sci 1983;24:1442–43.
  1. Lehrer MS, Sun TT, Lavker RM. Strategies of epithelial repair: modulation of stem cell and transit amplifying cell proliferation. J Cell Sci 1998;111:2867–2875.
  1. Tseng SCG. Concept and application of limbal stem cells. Eye 1989;12:201–9.
  1. Kruse FE Stem cells and corneal epithelial regeneration. Eye 1994;8:170–83.
  1. Pfister RR. Corneal stem cell disease: Concepts, categorization, and treatment by auto and homotransplantation of limbal stem cells. CLAO J; 20:64–72.
  1. Dua HS. Stem cells of the ocular surface: Scientific principles and clinical applications., Br J Ophthalmol 1995: 79:968–69.
  1. Hatch KM, Dana R. The Structure and Function of the Limbal Stem Cell and the Disease States Associated With Limbal Stem Cell Deficiency. Int Ophthalmol Clin 2009;49:43–52.
  1. Lee H, Khan R, O'Keefe M. Aniridia: current pathology and management., Acta Ophthalmol 2008;86:08–715.
  1. Ramirez-Miranda A, Zenteno JC. PAX6 gene intragenic deletions in Mexican patients with congenital aniridia. Mol Vis. 2006 Apr 7;12:318–23.
  1. Nishida K, Kinoshita S, Ohashi Y, et al. Ocular surface abnormalities in aniridia., Am J Ophthalmol 1995;120:68–375.
  1. Lopez-Garcia JS, Garcia-Lozano I, Rivas L, et al. Congenital aniridia keratopathy treatment.., Arch Soc Esp Oftalmol 2006;81:435–444.
  1. Ramaesh T, Collinson JM, Ramaesh K, et al. Corneal abnormalities in Pax6+ ⁄) small eye mice mimic human aniridiarelated keratopathy., Invest Ophthalmol Vis Sci 2003; 44:1871–1878.
  1. Fish R, Davidson RS Management of ocular thermal and chemical injuries, including amnioticmembrane therapy., Curr Opin in Ophthalmol 2010; 12:17–32
  1. Kim T, Khosla-Gupta A. . Chemical and Thermal Injuries to the Ocular Surface. In: Mannis MJ Holland EJ. Ocular Surface Disease -Medical and Surgical Management. Springer,  New York :  2002:100–113.
  1. Pfister R, Pfister D. Alkali-Injuries of the eye. In: Mannis M, Holland E, Krachmer M, eds. Cornea and External Disease: Clinical Diagnosis and Management. Mosby,  St. Louis :  2009: 443–1451.
  1. Tuft SJ, Shortt AJ. Surgical rehabilitation following severe ocular burns Eye 2009;23:1966–1971.
  1. Roper-Hall M. Thermal and chemical burns. Trans Ophthalmol Soc UK 1965;85:631–633.
  1. Davis AR, Ali QH, Aclimandos WA, Hunter PA. Topical steroid use in the treatment of ocular alkali burns. Br J Ophthalmol 1997;81:732–734.
  1. Jenkins C, Tuft S, Liu C, et al. Limbal transplantation in the management of chronic contact-lens associated epitheliopathy. Eye 1993;7:629–33.
  1. Pfister R, Haddox J, Paterson C. The efficacy of sodium citrate in the treatment of severe alkali burns of the eye is influenced by the route of administration. Cornea 1982;1: 205–211.
  1. Schwartz GS, Holland EJ Iatrogenic limbal stem cell deficiency. Cornea 1998;17(1):31–7.
  1. Tseng SCG, Chen JJY, Huang AJW, et al. Classification ofmconjunctival surgeries for corneal disease based on stem cell concept. Ophthalmol Clin N Am 1990;3:595–610.
  1. Krachmer J, Mannis MJ, MD, Holland EJ. Ocular Surface Transplantation. Cornea.2011 3rd. Edition. Elsevier  St. Louis;  2011: 456: 543.

  1. 34 Dua Hs, Miri A, Said SG. Contemporary limbal stem cell transplantation – A review., Clinical and Experimental Ophthalmology 2010;38:104–117.
  1. Jenkins C, Tuft S, Liu C, Buckley R. Limbal transplantation in the management of chronic contact lens-associated epitheliopathy. Eye 1993;5:629–663.
  1. Maharajan VS, Shanmuganathan V, Currie A, Hopkinson A, Powell-Richards A, Dua HS. Amniotic membrane transplantation for ocular surface reconstruction: indications and outcomes., Clin Experiment Ophthalmol 2007;35:140–7.
  1. Dua HS, Gomes JA, King AJ, Maharajan VS The amniotic membrane in ophthalmology., Surv Ophthalmol 2004;77:49–51.
  1. Ozdemir O, Tekeli O, Ornek K, Arslanpence A, Yalcindag NF. Limbal autograft and allograft transplantations in patients with corneal burns. Eye 2004;18:41–8.
  1. Henderson TR, Coster DJ, Williams KA. The long term outcome of limbal allografts: the search for surviving cells. Br J Ophthalmol 2001;85:604–9.
  1. Tsubota K, Satake Y, Kaido M et al. Treatment of severe ocular-surface disorders with corneal epithelial stemcell transplantation. N Engl J Med 1999: 340:1697–703.
  1. Reinhard T, Spelsberg H, Henke L et al. Long-term results of allogeneic penetrating limbo-keratoplasty in total limbal stem cell deficiency. Ophthalmology 2004;111:775–82.201.
  1. Dua HS, Al-Deiri B, Miri A. Long term Outcomes of Autolimbal and Allolimbal Transplants. 2010, Ophthalmology, Vol. 117, págs. 1207–1213.
  1. Geerling G, Maclennan S, Hartwig D. Autologous serum eye drops for ocular surface disorders. Br J Ophthalmol 2004;88:1467–74.
  1. Miri A, Al-Deiri B, Dua HS. Long-term outcomes of Autolimbal and Allolimbal transplants. Ophthalmology 2010;117:1207–1213.
  1. Liang L, Sheha H, Tseng SCG, et al. Long-term Outcomes of Keratolimbal Allograft for Total Limbal Stem Cell Deficiency Using Combined Immunosuppressive Agents and Correction of Ocular Surface Deficits. Arch Ophthalmol 2009,;127:1428–1434.
  1. Biber JM, Skeens HM, Neff KD, Holland EJ. The cincinnati procedure: technique and outcomes of combined living-related conjunctival limbal allografts and keratolimbal allografts in severe ocular surface failure. Cornea 2011;30:765–71.
  1. Sangwan VS, Basu S, MacNeil S, et al. Simple limbal epithelial transplantation (SLET): a novel surgical technique for the treatment of unilateral limbal stem cell deficiency., Br J Ophthalmol 2012;96:931–934.
  1. Liang L, Sheha H, Li J, Tseng SC. Limbal stem cell transplantation: new progresses and challenges. Eye 2009;10:1946–53.
  1. Ma DH, Kuo MT, Tsai YJ et al. Transplantation of cultivated oral mucosal epithelial cells for severe corneal burn. Eye 2009; 23:1442–1450.
  1. Chen HC, Chen HL, Lai JY et al. Persistence of transplanted oral mucosal epithelial cells in human cornea. Invest Ophthalmol Vis Sci 2009;50:660–4668.
  1. O'Callaghan A, Daniels JT. Concise Review: Limbal Epithelial StemCell Therapy: Controversies and Challenges. Stem Cells 2011;29:1923–1932.
  1. Traish AS, Chodosh J. Expanding Application of the Boston Type I Keratoprosthesis Due to Advances in Design and Improved Post-operative Therapeutic Strategies. Semin Ophthalmol 2010;25:239–243.
  1. Ament JD, Stryjewski TP, Ciolino JB, et al. Cost-effectiveness of the Boston keratoprosthesis., Am J Ophthalmol 2010; 149:221–228.
  1. Colby KA, Klufas MA. The Boston Keratoprosthesis. Int Ophthalmol Clin 2010; 50(3):161–175.
  1. Khan B, Dudenhoefer, Dohlman C. Keratoprosthesis: an update.. Ophthalmol 2001;12: 288–293.
  1. Sejpal K, Yu F, Aldave AJ. The Boston Keratoprosthesis in the Management of Corneal Limbal Stem Cell Deficiency. Cornea 2011; 30:1187–1194.