Medical Health Encyclopedia

The Procedure. In general the procedure is as follows:

• An implant, most commonly a 1/2 inch silicone tube, is inserted into the eye's front chamber (anterior). The Molteno implant used with mitomycin C is currently the most effective approach, with reported success rates of 80%. Other implants, such as the Ahmed implant, may have fewer complications.
• The tube drains the fluid onto a tiny plate that is sewn to the side of the eye.
• Fluid collects on the plate and then is absorbed by the tissues in the eye.

Complications. Complications include the following:

• Hypotony (very low eye pressure) is a serious complication that has been reduced using better techniques and improved implants.
• Cataracts, detached retina, breakdown of the cornea, and bleeding are potentially significant complications.
• There is also a risk for eye movement disorders, such as strabismus (crossed eyes) or diplopia (double-vision).

The implant often becomes blocked and repeated operations are needed. Some investigators are studying the use of a drug called tissue plasminogen activator (tPA) to open up tubes that have been blocked by blood or blood factors. (This so-called clot-busting drug is normally used to break up blood clots during heart attacks.) In one 2002 study, tPA prevented such blocks in 89% of eyes. Unfortunately, significant complications rates were high (11%).

Nonpenetrating Surgical Techniques: Deep Sclerectomy and Viscocanalostomy

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Deep sclerectomy and viscocanalostomy are less invasive techniques than filtering surgery that leave the anterior chamber (front of the eye) intact and avoid creation of blebs.

In deep sclerectomy, the surgeon removes a deep piece of the sclera (the white part of the eye), part of the trabecular meshwork, and the front of Schlemm's canal (the vessels that return fluid into the blood stream).

• In both deep sclerectomy and viscocanalostomy, the surgeon first creates a flap in the outer part of the sclera (the white part of the eye) and then removes a deep piece of the sclera underneath. This opens up Schlemm's canal (the vessels that return fluid into the blood stream) and exposes a layer above the anterior chamber called Descemet's membrane. A space has also been created between the inner and outer layers of the sclera.
• In deep sclerectomy, this space now serves as a tiny reservoir for aqueous fluid that flows now through the membrane and pools here. The fluid then flows out without the surgeon having to open the anterior chamber (as in standard filtering surgery).
• In viscocanalostomy, the surgeon typically injects gel-like materials into the ends of Schlemm's canal in order to enlarge the canal for fluid outflow and lower IOP. The tiny reservoir is sewn tightly up.