Surgical Technique 1 (Molteno Glaucoma Implant)

Delayed Drainage of Aqueous.

Delayed drainage of aqueous is used to control bleb fibrosis and was initially achieved by the two separate operation technique. In the first-stage operation, the plate of the implant was sutured to sclera and, instead of inserting the tube into the anterior chamber, the tube was tucked under a rectus muscle. Six to 8 weeks later, when the plate of the implant had become enclosed in a thin envelope of dense connective tissue, the free end of the tube was removed from beneath the muscle and inserted into the anterior chamber under a watertight scleral flap. This technique allowed the drainage area to be increased by linking 2–4 plates together in series. A clinical trial showed that four plates produced prolonged hypotony and suggested that the best compromise between avoidance of postoperative hypotony and good long-term IOP control was a double-plate implant (274 mm ² ).

Since 1986, the two separate operation technique has been replaced by the Vicryl tie technique. In this operation, the implant plate is sutured to sclera and then covered by Tenon's fascia. The tube is firmly tied and occluded by 5/0 Vicryl and then inserted into the anterior chamber via a self-sealing puncture wound. Thus, the IOP remains at its preoperative level until the tube spontaneously opens 3–5 weeks after operation. When the Vicryl tie dissolves, aqueous drains into a preformed bleb capsule lined by a thin layer of fibrous tissue 20–60 µm thick.

The intensity of inflammation and subsequent hypertensive phase depend on patient age and glaucoma severity. In infants aged less than 18 months and frail elderly patients without severe glaucoma, tube opening is followed by up to 3 weeks of low-normal IOP (10–15 mmHg) and then 3–4 weeks of moderately elevated IOP (25–30 mmHg). Subsequently, the IOP falls to normal levels ( Fig. 111-4 ). In severe glaucoma and young patients, the same sequence occurs except that the IOP rises sooner to 35–40 mmHg and the bleb vessels become visibly dilated. In these high-risk patients, this hypertensive phase can be suppressed by anti-inflammatory fibrosis suppression therapy and the occasional addition of hypotensive medication. The bleb then becomes pale and the IOP falls to normal levels.

Anti-Inflammatory Fibrosis Suppression Therapy.

Direct control of bleb fibrosis can be achieved using systemic anti-inflammatory agents. Initial trials of anti-inflammatory agents demonstrated that their effects could be detected by the resultant fall in IOP when given during the hypertensive stage of bleb inflammation. Significant anti-inflammatory effect was demonstrated with orally administered glucocorticoids, some nonsteroidal anti-inflammatory agents and colchicine. When given singly, none of these agents produced a marked effect. However, when given in combination these agents reduced postoperative bleb inflammation with its accompanying elevation of IOP and produced a thin-walled stable-stage bleb with excellent long-term IOP control.

The most effective combination of drugs identified to date is oral prednisone 10 mg, a nonsteroidal anti-inflammatory agent (e.g. diclofenac 50 mg) and colchicine 0.3 mg together with topical adrenaline 1–2% and topical atropine 1% all given three times daily for 5–6 weeks after operation (dosage as for a 70-kg healthy adult). Anti-inflammatory fibrosis suppression therapy is particularly advantageous in the most severe cases of glaucoma, such as when there is active intraocular inflammation. However, the development of surgical techniques for delayed aqueous drainage has greatly reduced the need for antifibrosis suppression.

Note that when using implants, this regimen should not be given before the onset of aqueous drainage as it prevents formation of a preformed bleb lining, delays the opening of the tube and increases the incidence of hypotony after the tube opens.

Delayed Versus Immediate Drainage of Aqueous.

Molteno implants can be inserted for delayed or immediate drainage of aqueous. The advantages of delayed aqueous drainage are such that the Vicryl tie technique is almost always used. Immediate drainage of aqueous, however, is necessary in acutely inflamed eyes and when immediate IOP reduction is required, e.g. acute neovascular glaucoma, uveitic glaucoma and when the eye contains blood after trauma. Photocoagulation of underlying retinal disease and/or anti-inflammatory fibrosis suppression therapy can be used to minimize the resulting hypertensive stage.

Delayed drainage allows time for tissues to heal and form a thin bleb capsule (preformed bleb) around the implant. During this time the IOP is controlled either with hypotensive medication or by making a relieving Sherwood slit in the side of the translimbal tube at the time of operation. The slit functions as a safety valve and releases aqueous if the IOP rises above normal levels. It ceases to function about 4 weeks after operation as the Vicryl tie dissolves and the tube opens allowing drainage of aqueous into the preformed bleb. This avoids postoperative hypotony, reduces the inflammatory response that occurs at the onset of aqueous drainage and results in a thinner bleb lining with superior long-term IOP control.

Quadrant Selection.

The superior nasal or superior temporal quadrants are preferred. Tenon's fascia is thicker in the superior nasal quadrant and minimizes the chance of late tube erosion through conjunctiva. Surgical exposure, however, is better in the superior temporal quadrant.

The inferior quadrants may also be used when superior quadrant access is limited. The inferior temporal quadrant is preferred in order to minimize the risk of diplopia that may occur in patients with good vision in both eyes if the inferior nasal quadrant is used.

In eyes containing silicone oil, the implant can be placed superiorly or inferiorly. Any silicone oil entering the tube drains to the bleb, and silicone oil that rarely blocks the ostium can be cleared with neodymium:YAG laser.