Ординатура / Офтальмология / Английские материалы / Glaucoma Surgery_Trope_2005

topical steroids. If severe, the tube may be repositioned or replaced. However, in most postoperative cases the cause for the persistent uveitis is unknown, and the treatment is that of any anterior uveitis in a glaucoma patient.

4.LATE POSTOPERATIVE COMPLICATIONS

4.1.Implant Drainage Failure

The most significant late complication is failure of the implant due to bleb fibrosis. Excision of the capsule with the application of an anti-metabolite such as mitomycin has been attempted but with moderate success. We do not recommend this approach. Placement of a second implant in a separate quadrant can lead to good success. J. Freedman, utilizes a supratenons position for the second implant with the view for trying to prevent fibrosis over the plate. This has been done with good success in a number of patients. Prevention of late encapsulation can be achieved by the use of fibrosis suppression medication as described by Molteno and colleagues (1,2). The medication consists of a nonsteroidal anti-inflammatory, a systemic steroid, colchicine and topical adrenaline. These medications need to be given no later than 14 days after insertion, and to be continued for 6 weeks thereafter. This systemic approach will need supervision by a rheumatologist or someone expert at dealing with the side effects of these toxic drugs. The removal and replacement of an existing implant is inadvisable, as fibrosis will occur very rapidly over the new implant.

4.2.Tube Erosion

Erosion of the tube through the sclera or overlying patch material can occur. This complication requires recovering of the tube with patch material, such as sclera or pericardium, to prevent the possibility of endophthalmitis from occurring. If the coverings fail to prevent recurring erosion of the tube, this is an indication to remove the tube from the eye (you can leave the plate) and a new implant should be inserted at a different site. Removal of the tube can be difficult as the tube is usually encased in a sleeve of connective tissue. When removing the tube, it is important to dissect carefully over the tube so as not to cut it, open the sleeve on its surface, and extend the opening to the limbus. Before removing the tube an 8/0 suture should be placed around the tube and the sleeve. On removal of the tube, the suture must be tied tightly to prevent the fistula from leaking. It is usually not necessary to remove the plate. The tube should be cut as close to the plate as possible and the plate should be left.

4.3.Plate Erosion

Erosion of the conjunctiva overlying the plate may occur especially if the tube is blocked purposely or accidentally. This allows the conjunctiva to constantly contact the plate, giving rise to the erosion. If there is a patent connection between the anterior chamber and the plate, in the presence of an erosion, the eye will become extremely hypotonous and the chances for endophthalmitis to develop are high. The best treatment for the erosion is to remove the implant. Erosions are more likely to occur in those cases where the conjunctiva over the implant has been treated with an anti-metabolite, particularly mitomycin C. Erosion through the conjunctiva is also more likely to occur if the original conjunctival incision is limbal based with the wound close to the plate. Erosions in such cases can be associated with epithelial down growth over the plate. This down

growth inhibits often repeated wound closure attempts including patch grafting necessitating removal of the plate and tube on occasion.

4.4.Diplopia

Limitation of eye movements may occur particularly in the presence of large blebs. As the plates are usually superiorly positioned, the limitation of movement is usually in upward gaze with little effect on the patient clinically. Placement of implants inferiorly is more likely to cause restriction of down-gaze with associated diplopia and such placement should be avoided if vision is good in both eyes (5). Certain implants may produce motility problems even if placed in the superior quadrants (3). Diplopia is common in the early postoperative period, but often resolves with time. Prisms are helpful if the diplopia is troublesome.

4.5.Corneal Decompensation

Another late complication of glaucoma implants is the development of corneal decompensation. This occurs particularly in aphakic and pseudophakic eyes. Many of these eyes have undergone previous glaucoma filtering procedures prior to the use of the glaucoma implant surgery, and these multiple surgeries invariably result in endothelial cell loss, added to by the further surgical trauma induced by the use of the glaucoma implant. It is possible that the silicone tube per se has some toxic effect on the endothelium, although this has never been proven. Extensive tube endothelial touch (direct touch or touch with eye movements) can precipitate endothelial cell decompensation in an eye with a low endothelial cell count. Corneal transplantation is needed when corneas decompensate. If it is well away from the endothelium, the tube needs to be left in situ. If the tube is close to the endothelium, a suture may be placed across the tube within the anterior chamber thus deflecting it away from the cornea (4). Alternatively, the tube may be repositioned prior to the penetrating keratoplasty. Other options include removing the tube and inserting a new valve in another quadrant, preferably before the corneal transplant (or in conjunction with the PKP). One of us (GT) has had success removing the tube from the anterior chamber repositioning it into the vitreous chamber, a maneuver requiring total vitrectomy, which potentially increases the morbidity of the procedure. Although not proven, this maneuver may prevent further corneal decompensation or allow for later corneal grafting.

In postpenetrating keratoplasty, two further complications can occur. The first of these is greater difficulty in controlling the glaucoma, as corneal transplants are often associated with the development of raised intraocular pressure. This is often seen even in the presence of a previously placed glaucoma implant. The second problem often seen is the development of a fibrous membrane seen covering the iris, as well as covering the intraocular lens. A possible cause is the formation of TGFb in the bleb, which then induces an inflammatory reaction in the anterior chamber. Management often requires removal of the membrane with total iridectomy and removal of the intraocular lens as well.

4.6.Other Complications

Although infrequent, complications that have been associated with glaucoma implants include retinal detachments (5), cataract formation, and the more serious complication of endophthalmitis. A rare form of sterile endophthalmitis is seen in glaucoma implants,

especially where an intratubal stent has been used to prevent postoperative hypotony (6). The cause is unknown.

Attention to meticulous surgical technique as well as adequate, frequent, and continued follow up of all glaucoma implant patients will result in a diminution of complications related to glaucoma implant surgery.

REFERENCES

1.Molteno ACB, Straughn JL, Ancker E. Control of bleb fibrosis after glaucoma drainage surgery. S Afr Med J 1976; 102:91 97.

2.Molteno ACB, Dempster AG. Methods of controlling bleb fibrosis around draining implants. In: Mills KB, ed. Glaucoma: Proceedings of the Fourth International Symposium of the North ern Eye Institute, Manchester, UK. Oxford: Pergamon Press, 1988:192 211.

3.Smith SL, Starita RJ, Fellman RL, Lynn JR. Early clinical experience with the Baerveldt 350 mm glaucoma implant and associated extraocularmuscle imbalance. Ophthalmology 1933; 100:914 918.

4.Freedman J. Management of the Molteno silicone tube in corneal transplant surgery. Ophthalmic Surg Lasers 1988; 29:432 434.

5.Waterhouse WJ, Lloyd MAE, Dugel PU et al. Rhegmatogenous retinal detachment after Molteno glaucoma implant surgery. Ophthalmology 1994; 101:665 671.

6.Ball SF, Latfield K, Scharfenberg J. Molteno ripcord suture hypopyon. Ophthalmic Surg 1991; 22:82 86.

Figure 9.2 (See color insert) The Ahmed valve is tucked underneath the limbral based conjunc tival flap.

3.2.Pars Plana Vitrectomy

Three-port pars plana vitrectomy is then performed by a vitreoretinal surgeon (Fig. 9.4).

3.2.1.The Infusion Port

In an aphakic or pseudophakic eye with the seton in the superotemporal quadrant, the infusion port is made through the inferotemporal limbus with a 20-gage MVR blade. An anterior chamber maintainer is inserted and the infusion is started once the tip of the infusion is in the anterior chamber. In a phakic eye, an inferotemporal sclerotomy is made with a 20-gage MVR blade 4 mm posterior to the limbus through a separate inferotemporal peritomy. A 7/0 vicryl suture is preplaced at the sclerostomy to facilitate closure at the

Figure 9.3 (See color insert) The Ahmed valve is anchored to the episclera with interrupted 8/0 silk sutures through the eyelets on the receptacle plate.

Figure 9.4 (See color insert) Sclerostomy is made with MVR blade 3 mm posterior to the limbus.

end of the vitrectomy. A posterior chamber infusion line is inserted, and the infusion started following confirmation that the tip of the infusion is in the vitreous cavity.

3.2.2.The Superotemporal Port

A superotemporal sclerostomy is made with a 20-gage MVR blade 3 mm posterior to the limbus in an apakic/pseudophakic eye or 4 mm posterior to the limbus in a phakic eye, at a location that is in line with the tube of the preplaced Ahmed Glaucoma Implant. This allows for the tube to be inserted into the pars plana through the same sclerostomy at the end of the vitrectomy. The placement of the superotemporal sclerostomy is therefore more superior than usual compared to a standard three-port pars plana vitrectomy.

3.2.3.The Superonasal Port

A superonasal sclerostomy is made with a 20-gage MVR blade 3 mm posterior to the limbus in an apakic/pseudophakic eye or 4 mm posterior to the limbus in a phakic eye, through a separate superonasal peritomy.

A complete vitrectomy is then performed. Particular attention must be paid to thoroughly remove the vitreous in the area of the tube insertion to prevent tube blockage by vitreous.

Air fluid exchange is then performed at the end of the vitrectomy. This is to ensure that the tube is “pneumatically stented” in the immediate postoperative period inside the vitreous cavity, preventing residual vitreous from plugging the pars plana end of the tube.

With the air-pump maintaining the intraocular pressure, the superonasal port is plugged with a scleral plug. Attention is now turned to the placement of the tube into the pars plana.

3.3.Placement of the Pars Plana Tube

The Pars Plana ClipTM is slide along the tube until the “bend” is at the correct distance for insertion through the superotemporal sclerostomy (Fig. 9.5).

Figure 9.5 (See color insert) Set up for Pars Plana sclerostomy with Landers ring suture in place.

Excess amount of tube is trimmed so that the tube extends 5 mm into the vitreous cavity when inserted through the sclerostomy.

After inserting the tube through the superotemporal sclerostomy, the sclerostomy is narrowed with an interrupted 10/0 nylon to ensure that the sclerostomy is water-tight around the tube (Fig. 9.6).

The Pars Plana ClipTM is then anchored to the episclera with interrupted 8/0 silk through the two eyelets (Fig. 9.7).

3.4.Closure

The Ahmed Glaucoma Valve tube and Clip is then covered by a graft of eye bank cornea, sclera, or other material. If cornea is used, it should be prepared in

Figure 9.6 (See color insert) The tube of the Ahmed valve is inserted through the superotemporal sclerostomy.