Principles of Vitrectomy

P Mahesh Shanmugam

Section I

Surgical Management of Vitreoretinal Diseases

Principles of VitrectomyChapter 1

P Mahesh Shanmugam

(India)

INTRODUCTION

Closed vitrectomy was introduced in the 1970s by Dr Machemer. The essential principle of closed vitrectomy is to remove as much vitreous as possible with least trauma to the other intraocular structures, particularly the retina.¹ Vitreous surgery is usually performed to clear media opacity, relieve traction on the retina and allow access to the retina for additional surgical techniques.^2,3 Various techniques individually or in combination in differing sequences may be necessary in a given case to tackle the underlying vitreoretinal problem.

BASIC PRINCIPLES

Vitreous surgery is performed through watertight incisions to maintain intraocular pressure at a suitable range. Placement of incisions is such that, instruments can enter the eye easily, can be manipulated within the eye and also allows movement of the eye in different directions, thereby permitting maximal access to the vitreous cavity.

Vitreous surgery by default needs optimal visualization of the vitreous and the retina making wide pupillary dilatation mandatory.

Visualization of the posterior compartment for vitreous surgery is achieved using specialized lens systems.

Care is taken to avoid corneal epithelial injury by drying or trauma by keeping it hydrated or a viscoelastic coupling.

Vitrectomy involves sucking and cutting tiny pieces of the vitreous gel with utmost care to minimize the effect of tractional forces on the retina.

The surgery is completed as rapidly as possible and damage to adjacent normal tissue is avoided.

The anatomic and mechanical objectives of vitrectomy are achieved in a specific sequence to minimize the risks associated with certain complex maneuvers and facilitate prompt treatment of complications.

OBJECTIVES OF VITRECTOMY

The objectives of surgery differ in each case depending on the disease being treated.^2-5

The schema for two of the commonest indications for vitrectomy, rhegmatogenous retinal detachment and proliferative vascular retinopathy is as follows:

SURGICAL STEPS OF VITRECTOMY

Preoperative Preparation

Dilation of the pupil with 10% pheylephrine and 1% tropicamide drops. Phenylephrine is substituted with 1% homatropine in hypertensive patients. Preoperative antibiotic use for 3 days prior to surgery is preferable. Preoperative povidone iodine (5%) is applied in the conjunctival sac and allowed to stay for 5 minutes prior to surgery.

Six hours of preoperative fasting is advised for patients undergoing surgery under general anesthesia and 1½-2 hours if under local anesthesia. The medications for systemic diseases are not discontinued on the day of surgery except for the antidiabetic medication.

Anesthesia

Most vitreoretinal surgeries can be completed using peribulbar or retrobulbar anesthesia.⁶ Parabulbar anesthesia can be used for intraoperative supplementation if needed.⁷2

Flow chart 1: Surgical steps in vitrectomy

General anesthesia may be employed when surgery is planned for children, uncooperative patients and for long procedures.

Positioning of the Patient

The patient is positioned as for any intraocular surgery with the eye in parallel plane to the operating table. The face of the patient may be turned to the opposite side to prevent the nose of the patient from coming in the way of surgery.

Vitreoretinal procedures are performed using the operating microscope with the surgeon seated comfortably erect to prevent fatigue during the long surgical procedures.

Conjunctival Opening

Limited opening, involving 30° nasally and 90° temporally if the surgical procedure does not require scleral buckling is adequate for exposure for vitrectomy; if buckling is to be performed, the conjunctiva is opened 360°, most often at the limbus, and paralimbally in case of perilimbal scarring (Fig. 1).

A large majority of vitrectomies are currently performed using the transconjunctival technique using the 23 gauge or less commonly the 25 gauge systems. The transconjunctival surgery allows placement of the sclerotomies without the need place a conjunctival opening.

Sclerotomy

The scleral incision in to the eye for vitreoretinal surgery, called sclerotomy enters the eye through the pars plana in adults.3

Fig. 1: Intraoperative photograph showing limited limbal conjunctival opening for 20 gauge vitrectomy. Nasal conjunctiva is opened 30° (white line) and the temporal 90° straddling the lateral rectus (black line)

Fig. 2: Sclerotomies are placed at 3-3.5 mm in aphakic or pseudophakic adults and at 3.5-4 mm in phakic adults

Fig. 3: Intraoperative photograph showing anterior sclerotomy (1 mm from limbus) in an infant with stage 5 ROP

Fig. 4: Intraoperative photograph showing technique of placing the 23 gauge cannula for transconjunctival pars plana vitrectomy. The trocar loaded with the cannula is inserted obliquely into the sclera to create a self-sealing sclerotomy

Fig. 5: Intraoperative photograph showing 23 gauge infusion cannula (textured arrow); superotemporal and nasal cannulae (plain arrows) with plugs in place

Fig. 6: Intraoperative photograph showing placement of the infusion cannula in a 20 gauge vitrectomy, the cannula being secured with a preplaced suture and a slip knot. The superior sclerotomies are temporarily closed using scleral plugs

Pars plana extends from pars plicata which extends 2 mm posterior to the limbus. Pars plana extends posteriorly 3 mm from pars plicata (5 mm from limbus) nasally and 5 mm (7 mm from limbus) temporally. Sclerotomies are placed 3-3.5 mm from the limbus in aphakic or pseudophakic patients and 3.5-4 mm in phakic patients (Fig. 2). Such a placement will avoid inadvertent damage to the lens anteriorly and be sufficiently away from the vitreous base which straddles the ora for 3-4 mm. Sclertomies are placed in the pars plicata (thereby anteriorly) in infants and children where the pars plana is ill developed (Fig. 3). A 20 gauge sclerotomy accommodating 20 gauge instruments is commonly used for vitrectomy. The newer transconjunctival trocar cannula systems use the 23 or 25 gauge instruments (Fig. 4).

Three sclerotomies are used for a routine vitrectomy. Two are placed in the superior quadrant and are used to perform the surgical maneuvers. The other sclerotomy placed at the lower border of the lateral rectus is used to place the infusion cannula through which balanced salt solution or ringer lactate solution is infused in to the eye to replace the vitreous being removed (Fig. 5). The infusion cannula in 20 gauge vitreous surgery is secured using a preplaced suture and a slip knot (Fig. 6).

This placement allows for the infusion tubing to drape downacross the patient's lateral canthus area and also prevents the cannula coming in to contact with orbital bones leading to kinking of the cannula within the eye leading to possible lens damage. The active sclerotomies are placed 140-150° apart in the superonasal and superotemporal quadrants at the superior border of the lateral and medial rectus muscles (Fig. 7). Such a placement allows for comfortable hand placement during bimanual vitrectomy for the surgeon and keeps the instruments in each hand from hitting each other outside the eye and causing inadvertent damage to the delicate intraocular structures.

Lens Removal

The lens, if cataractous, may have to be removed during vitreoretinal surgery to facilitate visualization for surgery or earlier patient rehabilitation in the postoperative period. A clear lens may also be removed to facilitate access to the vitreous base region in certain vitreoretinal procedures such as giant retinal tear repair, anterior proliferative vitreoretinopathy, penetrating injury and retinopathy of prematurity.

The lens is removed with the vitreous cutter itself if soft and using the ultrasonic fragmentor, if hard (Fig. 8). Very hard lenses are removed by intracapsular or extracapsular cataract surgical techniques. It is essential to have water tight closure of the limbal would to facilitate vitreous surgery.

In patients, undergoing vitreous surgery for diseases other than rhegmatogenous retinal detachment, such as for clearing the vitreous hemorrhage, phacoemulsification with intraocular lens implantation may be performed along with vitreoretinal surgery.

Visualization

Wide angle viewing systems using high plus non-contact or contact lenses are used to view the fundus during vitreous surgery. These lenses create a real, inverted image that is inverted to form an erect image using an inverter incorporated in to the operating microscope (Fig. 9). Landers lenses and irrigating contact lenses are other options for visualization of the fundus (Figs 10 to 12).

Vitrectomy

The aim of vitrectomy is to safely remove as much of the vitreous as possible without damage to other intraocular structures, particularly the retina. This is achieved by employing a low suction, high cut rate technique wherein tiny portions of the vitreous are sucked into the cutter and excised so that the pull on the vitreous is not transmitted to the retina.

The sequence of vitrectomy is to start with anterior vitrectomy including excision of the anterior hyaloid face in aphakic patients. In phakic patients, the vitreous adjacent to the posterior capsule of the lens is spared to avoid iatrogenic lens damage. The mid and posterior vitreous are then removed (Fig. 13). If the posterior hyaloid is detached and taut held by its attachment to the disc and the vitreous base, the subposterior hyaloid face is entered where there is maximum separation from the retina. The posterior hyaloid is then trimmed circumferentially and the anterior vitreous is trimmed up to the vitreous base as much as possible avoiding lens damage in phakic patients (Fig. 14). If the posterior hyaloid is not detached from the retina, its detachment is induced and then excised (Fig. 15).

Special Techniques

Removal of nonclotted blood: Nonclotted blood is removed using an instrument called the flute. This instrument has a hollow bore vented to the atmosphere. The increased pressure (as compared to the atmospheric pressure) within the eye due to gravity dependent flow of fluid in to the eye creates a pressure gradient that pushes the fluid within the eye out, through the flute.⁸5

Fig. 7: Intraoperative photograph showing technique of 3 port 23 gauge vitrectomy. Self-retaining infusion cannula is placed in the inferotemporal quadrant. The surgeon holds the light pipe for illuminating the vitreous cavity in the non-dominant hand (left hand in the picture above) and the vitreous cutter or other active instrument in the dominant hand. The instruments are introduced through the superonasal and superotemporal sclerotomies to perform vitreous surgery

Fig. 8: Intraoperative photograph showing lensectomy in progress. Lensectomy is performed to treat congenital cataract or to aid vitreous surgery in young patients with cataract or anterior PVR. Lensectomy can be performed using vitreous cutter in infants and children with a soft lens. An ultrasonic fragmatome is used to remove harder lenses in adults

Fig. 9: Binocular indirect operating microscope (BIOM)

Fig. 10: Intraoperative photograph showing ring (arrow) used to hold the Landers lens set for fundus visualization in place. 23 gauge infusion cannula and superior cannulae with plugs in place can also be seen

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The vent of the flute needle allows the surgeon to control the flow of the fluid (Figs 16 and 17).
Separation or segmentation of epiretinal membrane: Nonvascularized membranes are separated from the retina using a pick or a spatula. The separated edge is then grasped with an intraocular forceps and the membrane is “peeled” off the retinal surface using force tangential to the surface (Figs 18 to 20). Vascularized membranes as seen in proliferative vascular retinopathy usually have underlying vascular “nails” anchoring them to the retina in various places. Contraction of the vitreous between two vascular nails leads to bridging traction. This traction can be relieved by cutting across this bridging traction using the vitreous cutter or vitreoretinal scissors–segmentation⁹ (Figs 21 to 23). In toto removal of the membrane by dissecting under the vascular membrane, cutting all the nails using a fine sharp pointed scissors is called delamination^2,4,5 (Figs 24 to 26). Bimanual dissection may be necessary when the membranes are adherent densely with numerous vascular nails (Fig. 27).
Achieving hemostasis: Intraocular hemorrhage may occur from the retinal surface, pars plana or bare choroid, during vitreoretinal surgery. The most commonly used technique to stop bleeding is to elevate the infusion bottle there by increasing the intraocular pressure to tamponade the bleeding vessel. Persistent bleeders may be sealed using intraocular bipolar diathermy. Diathermy can also be used to mark the retinal breaks for later identification. Thrombin solution may also be used in the infusion fluid to achieve hemostasis.^10,11
Evacuation of subretinal fluid: Subretinal fluid is removed using the flute needle placed at a retinal break. Air from an automated pump is used to push the intravitreal and subretinal fluid out of the eye through the flute needle^8,12 (Figs 28 and 29). If all the traction has been removed from the retina, the air does not enter the subretinal space but tamponades the break and pushes the retina towards the retinal pigment epithelium (RPE), resulting in retinal reattachment. In patients with rhegmatogenous retinal detachment, tamponade for a longer duration may be necessary for which gases or oil may be used.^13,14 The most commonly used gases are sulphur hexafluoride and perfluropropane as a non-expansile mixture (Fig. 30). Silicone oil is used if long-term tamponade is desired. Presence of intravitreal gas does not allow the patient to see until it is absorbed and in these situations, silicone oil is preferable for early visual rehabilitation, particularly in one-eyed patients. When using silicon oil for tamponade in an aphakic eye, an inferior peripheral iridectomy is performed to prevent pupillary block due to the oil¹⁵ (Fig. 31). Fluid gas exchange can also be used to stop intraocular bleed. Gas inside a phakic or pseudophakic eye leads to difficulty in Intraoperative visualization of the fundus and high minus lenses have to be used to neutralize this optical system.¹
Treatment of retinal breaks: Once the retina is opposed to the RPE, chorioretinal adhesion can be created around the retinal break using laser photocoagulation or cryopexy (Figs 32 and 33). Air acts as an insulator and hence lower power is adequate to create a reaction with laser of cryo in an air filled eye.^17,18 Endolaser can also be used for panretinal photocoagulation, treat ciliary process for control of glaucoma, stop bleeders from retinal surface and also to coagulate epithelial ingrowth on the iris, and ciliary body (Fig. 34).
Retinotomy/retinectomy:^2,4,19 A retinotomy is creation of a hole in the retina and may be performed to access the subretinal space to remove subretinal bands or for drainage of the subretinal fluid when the original break is not accessible or seen. Retinectomy is usually performed to relieve severe traction that persists despite epiretinal membrane removal. It is also performed to relieve traction caused by fibrovascular ingrowth secondary to penetrating eye injury. Retinotomy and retinectomy are performed after demarcating the site with diathermy. Retinotomy is usually performed using the intravitreal scissors while retinectomy may be performed using the vitreous cutter (Figs 35 and 36). Perfluorocarbon heavy liquid may be used to keep the posterior retina attached during relaxing retinotomy. Perfluorocarbon heavy liquid is also used to reattach the retina after relaxing retinotomy or to reattach a giant retinal tear associated retinal detachment (Fig. 37).
Internal limiting membrane removal may be necessary as part of vitrectomy in managing diffuse diabetic macular edema, macular hole surgery, etc. Triamcinolone crystals, indocyanine green brilliant blue can all be used to visualize the internal limiting membrane to aid its removal (Figs 38 and 39). Triamcinolone can also help visualize abnormal vitreoretinal adhesions and the posterior hyaloid face.
Scleral buckling: An encircling element or scleral buckling is used in addition to vitrectomy to support the vitreous base and relieve residual traction on the retinal breaks.^2,20
After completion of the surgery, the sclerotomy sites are examined with the indirect ophthalmoscope to ensure the absence of sclerotomy related complications.7

Fig. 11: Intraoperative photograph showing Landers lens used to visualize posterior fundus. The refractive power of the cornea and the lens has to be neutralized to facilitate visualization of the fundus for vitreous surgery

Fig. 12: Intraoperative photograph showing Landers prism lens used to visualize peripheral fundus. Convex Landers lenses are used to visualize various areas of the fundus during vitreous surgery. To neutralize the high plus power of the eye when vitreous cavity is filled with air, concave Landers lenses are used

Fig. 13: Intraoperative photograph showing mid vitrectomy. Vitrectomy progresses from anterior to posterior. After removal of the core vitreous, posterior vitreous detachment is induced if not present. Posterior hyaloid is entered in the superonasal quadrant and the anteroposterior traction is relieved by circumcising the vitreous. The posterior vitreous is dissected off its attachments and removed. Anterior vitreous is trimmed up to the vitreous base

Fig. 14: Figure depicting circumcision of the partially detached vitreous. The posterior vitreous face is opened in an area where it is highly detached from the retina and the opening is extended circumferentially, separating the posterior vitreous from the attachment of the anterior vitreous to the vitreous base. The posterior vitreous is then removed by cutting towards the posterior pole and the anterior vitreous skirt trimmed towards the vtireous base as much as safely possible

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Fig. 15: Intraoperative photograph showing induction of posterior vitreous detachment (arrow) in a patient with proliferative diabetic retinopathy. The posterior vitreous is peeled off from the retina using the vitreous cutter or silicone tipped cannula, employing active suction. A forceps can also be used to peel the vitreous attached to the disk

Fig. 16: Aspiration of loose pre-retinal blood using the flute needle. Flute needle aspiration is passive aspiration as intraocular pressure during vitrectomy is higher due to gravity or forced infusion into the vitreous cavity than atmospheric pressure.

Fig. 17: Intraoperative photograph showing aspiration of loose pre-retinal blood using the flute needle

Fig. 18: Technique of peeling epiretinal membranes using a retinal pick in retinal detachment complicated by proliferative vitreoretinopathy

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Fig. 19: Intraoperative photograph showing tangential peeling of pre-retinal membranes in PVR

Fig. 20: Intraoperative photograph showing peeling of membranes in retinal detachment complicated by proliferative vitreoretinopathy. A forceps is used to grasp and peel the membranes in a tangentially oriented fashion

Fig. 21: Technique of segmentation wherein the fibrous tissue is cut in to islands thereby removing tangential traction. This technique is particularly useful in the management of tractional retinal detachment in vascular retinopathies

Fig. 22: Intraoperative photograph showing technique of segmentation. One blade of the intravitreal scissors is introduced between the fibrous tissue and the underlying retina and the other blade over the fibrous tissue

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Fig. 23: Intraoperative photograph showing immediate post-segmentation appearance. The fibrous tissue is cut in to islands (arrow) thereby relieving tangential bridging traction between adjacent areas of the retina

Fig. 24: Technique of delamination wherein the vascular nails anchoring the fibrous tissue to the underlying retina are cut and the fibrous tissue is removed in toto

Fig. 25: Intraoperative photograph showing delamination technique. The vascular nails anchoring the fibrous proliferation to the retina are dissected to allow complete removal of the fibrous tissue. This technique is often employed in diabetic vitrectomy

Fig. 26: Intraoperative photograph showing delamination technique of fibrous tissue dissection. As seen in the photograph, both blades of the vitreous scissors are introduced below the fibrous tissue to cut the vascular nails

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Fig. 27: Intraoperative photograph showing bimanual membrane dissection in a child with stage 5 ROP. The forceps is used to hold the tissue and a scissors to dissect the tissue. Posterior bimanual dissection can be performed using illuminated instruments or by placing a fourth vitrectomy port. Chandelier illumination systems can then be introduced through the fourth port or the assistant can hold the light pipe, allowing the surgeon to perform bimanual dissection

Fig. 28: The flute needle is placed over the retinal break and the air bubble expanding from the anterior vitreous pushes the retina towards the retinal pigment epithelium. The subretinal fluid trapped between the retina and RPE escapes through the flute needle out of the eye resulting in retinal reattachment

Fig. 29: Intraoperative photograph showing internal drainage of subretinal fluid

Fig. 30: Intraocular tamponade with nonexpansile gas mixture. The gas bubble (shaded circle) floats and closes the retinal break due to surface tension of the gas bubble across the retinal break. As gas bubble floats and also absorbs overtime, it is used for tamponading superior retinal breaks. Inferior retinal breaks are better tamponaded using silicone oil

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Fig. 31: The need for inferior peripheral iridectomy in aphakic silicone oil filled eyes. Silicone oil also floats and the aqueous collects in the inferior part of the vitreous cavity with the patient in erect position. An inferior iridectomy allows access of this aqueous pocket to the anterior chamber angle

Fig. 32: Technique of retinopexy using endolaser after fluid air exchange and reattachment of the retina

Fig. 33: Intraoperative photograph showing rows of endolaser along the borders of a giant retinal tear. The posterior glistening reflex is due to perflurocarbon liquid temporary tamponade

Fig. 34: Intraoperative photograph showing endolaser being performed. Endolaser can be delivered through 20 or 23 gauge sclerotomy openings

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Fig. 35: Technique of circumferential relaxing retinotomy. Note perflurocarbon bubble used posteriorly to keep the posterior retina attached

Fig. 36: Intraoperative fundus photograph showing relaxing retinotomy. Relaxing retinotomy is usually performed to isolate posterior retina from contracted anterior retina. The border of the retinotomy is cauterized and intravitreal scissors is used to cut the retina

Fig. 37: Technique of reattaching the retina using perfluorcarbon liquid. As PFCL is heavier than water, it sinks inside the vitreous cavity to reattach the retina and is particularly useful in giant retinal tear surgery. Using air to reattach the retina in giant retinal tear or following relaxing retinotomy can result in retinal folds that may hamper visual recovery

Fig. 38: Intraoperative photograph showing triamcinolone injection in to the vitreous cavity. Triamcinolone crystals entangle in the vitreous fibers enabling visualization of the clear vitreous. Fluorescein has also been used to stain the vitreous to enable identification of abnormal vitreoretinal adhesions and complete vitrectomy

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Fig. 39: Intraoperative photograph showing identification of the internal limiting membrane using triamcinolone. Triamcinolone deposits on the internal limiting membrane aiding peeling of the ILM. The demarcation between retina bereft of ILM and persistent ILM can be seen (dotted line). Indocyanine green, tryphan blue, brillant blue are stains that can be used to stain the ILM and aid its peeling

Fig. 40: Intraoperative photograph showing technique of conjunctival closure using bipolar cautery—the edges of the conjunctiva are held together and cauterized for apposition

Fig. 41: Intraoperative photograph showing appearance at conclusion of 20 gauge vitrectomy. The conjunctiva was closed with bipolar cautery avoiding suture associated irritation, discharge

Fig. 42: Intraoperative photograph showing technique of removing 23 gauge cannula at conclusion of surgery. The cannula is removed along the direction of its insertion and the port kept occluded with cotton tip applicator for 30 seconds to allow closure of the sclerotomy

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Fig. 43: Intraoperative photograph appearance at conclusion of 23 gauge transcleral sutureless vitrectomy. The conjunctival and scleral entry is not visible

The sclerotomies are closed with absorbable sutures achieving water tight closure. The conjunctival incision is closed with absorbable suture or using bipolar cautery (Figs 40 and 41). In 23 or 25 gauge transconjunctival vitreous surgery, the cannula is removed along the direction of its insertion allowing self-sealing of the scleral and conjunctival incisions^21,22 (Figs 42 and 43).

REFERENCES

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Chapter Notes

Principles of VitrectomyChapter 1