Glaucoma Ashok Garg, Emanuel Rosen, Tanuj Dada, Ahmed K Khalil
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1CLINICAL GLAUCOMA

Early Onset Developmental Glaucoma (Primary Congenital Glaucoma)1

Ahmad K Khalil
(Egypt)
 
INTRODUCTION
Developmental glaucoma is a glaucoma caused by maldevelopment of the eye's aqueous outflow system. Depending on the severity of this maldevelopment the resultant elevated intraocular pressure may occur at birth or anytime thereafter. Most cases present at birth (congenital) or within the first year of life (infantile), and on these entities, we refer as early onset developmental glaucoma (EODG). Due to the elastic nature of the embryonic tissues, the eye ball stretches and enlarges in congenital cases, with subsequent Descemet's membrane ruptures, corneal edema and cloudiness. Pressure on the elastic optic nerve head and lamina cribrosa leads to early (distension) cupping, but eventually functional loss and glaucomatous optic atrophy ensue.
The disease is bilateral in 75% of the cases, males more commonly affected (65%). There is sporadic occurrence in 90% of the cases, the remainder; autosomal recessive with variable penetrance. Its incidence is 1:10,000 births in the West and 1:2500 births in the Middle East. More than 80% present before 1 year.
Genetically, EODG appears to be a genetically heterogeneous disorder in that there is an unequal sex distribution and fewer numbers of affected siblings. To date, 2 loci have been found for EODG: GLC3A (chromosome 2p21) and GLC3B (chromosome 1p36).
 
CLINICAL SIGNS AND SYMPTOMS
Epiphora, photophobia and blepharospasm are often the first symptoms to alarm the parents. Any of these symptoms warrants careful examination with glaucoma in mind. I have seen infants with a moderate degree of glaucoma who were referred because of persistent epiphora after nasolacrimal probing.
Grayish discoloration (cloudiness of the cornea) is usually the presenting symptom of more advanced cases.
Corneal enlargement without cloudiness is a less often presenting symptom, as it is often thought by parents as a beauty sign, rather than an abnormal alerting sign.
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Fig. 1: Classically described EODG with photophobia, epiphora, corneal enlargement and cloudiness
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Fig. 2: Parents are often peaceful with larger corneas of their infants seeing it as a sign of beauty, and often overlooking the mild corneal cloudiness seen in the right eye of this infant
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EXAMINATION
The normal IOP in the newborn well falls in the 1 digit mmHg readings. The disc has almost no cup. The cornea is clear, its horizontal diameter in a fullterm newborn is 10 to 10.5 mm and increases to the adult diameter of approximately 11.5 to 12 mm by 2 years of age.
 
IOP
Examination is ideally done under general anesthesia, where it would be possible to make a full examination at no haste. This is at least necessary for a first full examination for decision making and a couple of follow up examinations as thought necessary. Follow up examinations can then adequately be made with sedation (chloral hydrate), and with proper training afterwards, without sedation as early as the second year of life.
Most general anesthetics tend to lower IOP readings, and a knowledge of the anesthetic used and its behavior is needed. A hand-held applanation tonometer, is a good device in this regard. Lid and canthal pressure can lead to false high IOP readings with forceful opening of the eye lids.
 
Cornea
Using the surgical microscope or a portable slit lamp, early corneal edema or more pronounced clouding and breaks in Descemet's membrane should be looked for. A diameter greater than 12 mm in an infant is highly suggestive of EODG. Developmental anomalies of the cornea and iris must be noted because they may alter diagnosis and treatment. Corneal clouding is usually reversible after IOP control.
Rupture lines of Descemet's membrane (Haab's striae) with associated localized areas of edema can be seen in moderate to severe untreated cases. Glassy lines can be seen long after glaucoma control, and might be the only indication of self limited IOP rise episodes in infancy.
 
The Optic Nerve Head
A cup/disc ratios greater than 0.3 in an infant is suggestive of glaucoma. Changes in the optic disc occur readily with changes in IOP in infants due to increased tissue elasticity which translates IOP increase into mechanical distortion in the disc supporting elements. Globe enlargement further magnifies this mechanical cupping. This cupping is easily reversible typically within 4–6 weeks after normalization of IOP. The younger the child, the faster the reversibility. If left untreated, neuronal loss eventually ensues, with irreversible damage. Together with regression of photophobia, reversibility of optic disc cupping is one of the best criteria for surgical success in most cases.
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Fig. 3: Measuring the IOP under general anesthesia using the Perkins tonometer in the operation theater. For follow up examinations, a mask anesthesia with an oral airway is usually adequate
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Fig. 4: Measuring of the white to white corneal diameter
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Gonioscopy
Gonioscopy is performed by use of a gonioprism, a Koeppe or a barkan operating lens (a truncated koeppe lens) and binocular microscope for the evaluation of goniodysgenesis.
 
Axial Length Measurements
Measuring the axial length was proposed as a diagnostic and follow-up procedure. It is generally thought, however that corneal diameter is a more sensitive tool in this context.
 
Differential Diagnosis
Mild to moderate cases can easily be confused by entities which increase corneal diameter (megalocornea), cases with corneal cloudiness (sclerocornea, dystrophies like Meesman's and Reis-Buckler), or other causes of epiphora (NLD obstruction).
 
MANAGEMENT
Surgery is the first line of therapy for EODG for the following reasons: 1) Since this type of glaucoma results from abnormal anatomical development of the anterior chamber angle, anatomical or surgical correction is recommended. 2) Accumulated experience shows the effectiveness of surgery. 3) It is difficult to determine the effectiveness of medical therapy in infants and children because the procedure is complicated and may require anesthesia. The long-term effectiveness and complications of different anti-glaucoma drugs have not been well studied.
 
Surgical Management
Trabeculotomy and goniotomy remain the first line surgical procedures for EODG. They directly attack the faulty site with minimal surgical trauma, as compared with trabeculectomy, hence inviting much less tissue reaction and fibrosis which very often compromise the surgical outcome. The absence of external aqueous filtration precludes delayed filtering bleb-related complications, such as infection, hypotony, and leaks.
Trabeculotomy and goniotomy seem to be in some ways equivalent, and both are particularly successful in previously unoperated cases of EODG. Goniotomy, however, does not have a good success rate when done below 1 month or over 2 years of age. It is usually associated with a relatively high rate of recurrence, and multiple goniotomies are needed to achieve a success rate similar to that of trabeculotomy. Trabeculotomy is probably a more demanding technique with which it may be more difficult to achieve a technically perfect procedure than it is with goniotomy, but it is the preferred choice of the author of this chapter, with a 5-year cumulative success rate of 92%.
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Fig. 5: Corneal cloudiness clearing in the left eye 5 days after surgery as compared to the right still cloudy non-operated eye (watering is caused by child crying rather than epiphora)
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Fig. 6: Rupture lines of Descemet's membrane (Haab's striae) with associated localized areas of edema
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Goniotomy involves the creation of a superficial incision into uveal TM, allowing the iris root to move posteriorly and presumably relieving the mechanical obstruction to aqueous outflow. This procedure is performed under direct visualization through a gonioscopic contact lens and the operating microscope.
Trabeculotomy is my first choice for surgery in all cases of EODG, regardless any previous surgery, as long as there is a sound non-scarred 120 degrees of limbic circumference. A properly performed trabeculotomy gives good results in most of these eyes. Bad prognostic signs include; eyes with corneal diameter 14.5 or more, advanced congenital cases, and multiple previous surgeries. It involves creating a superficial sclera flap and then making a limbal radial incision to reach and incise open the Canal of Schlemm, which is then probed on either side by specially designed probes. When these are rotated into the AC, they sever the malformed trabecular/angle tissue.
Trabeculectomy: The decision to perform this procedure must be made carefully because in infants and children, filtering bleb formation may be difficult despite intraoperative use of antimetabolites. Even after filtering blebs are successfully formed, the patients may be exposed to the risk of postsurgical infections for the rest of their life.
 
Deep Sclerectomy
No much role as it leaves the trabecular beams, which are the main site for resistance to outflow in EODG, untouched.
 
Aqueous Shunt Implantation
The enhanced success with aqueous shunt devices is associated with a higher likelihood of postoperative complications. They can probably used as a last resort in refractory cases with multiple previous surgeries and compromised angle structures.
 
MEDICAL TREATMENT
Because of poor efficacy, a greater potential for adverse systemic side effects, medical treatment is used as an auxiliary means to temporarily control IOP till surgery is performed or in the rare instance when repeated surgeries fail to control IOP. Brimonidine should be used with caution in young children because of the potential for CNS depression.
 
Prognosis
Even after successful surgery with IOP control and regression/stabilization of optic disc cupping, regular follow-up and rehabilitation measures will be necessary to achieve a favorable outcome and prognosis. It is near meaningless to save an eye from sight threatening glaucoma, and lose it.
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Fig. 7: The second trabeculotomy probe is being rotated into the AC
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Figs 8A and B: 3 years after bilateral successful trabeculotomy for EODG, this case presented with anisometropia (one eye myopic, the other low hyperopic) and strabismus. Glasses correction and amblyopia management could achieve a bilateral 0.8 visual acuity