Surgery to Treat Glaucoma
Approximately 10 percent of people with open-angle glaucoma undergo surgery because of serious side effects from medications they were taking, lack of response to drug treatment, an inability to take their medications properly, or medical conditions or allergies that interfere with drug therapy.
Although surgery cannot restore lost vision, it can reduce IOP by improving drainage of aqueous humor. As a result, surgery can dramatically slow the progression of optic nerve damage and vision loss. The most common surgical procedures for open-angle glaucoma are laser trabecular surgery and filtration surgery.
Laser trabecular surgery
In this procedure, approximately 80 to 100 tiny laser burns are made in the area of the trabecular meshwork. The procedure increases the drainage of aqueous humor, most likely by stimulating the activity of trabecular cells. The procedure takes about 15 minutes and is performed on an outpatient basis, using eyedrops for anesthesia. IOP must be measured one hour after surgery because it may temporarily rise as a result of the treatment. Postoperative complications are minor and include eye inflammation, blurred vision, and minimal discomfort, usually lasting for about 24 hours.
It takes up to six weeks to determine whether the procedure has been effective. IOP-lowering medication is often still required after surgery, but if the procedure reduces IOP considerably, you may be able to lower the dose of your medication. As with many treatments, however, the effect of surgery diminishes with time in some people. About 40% of individuals need additional medication or some other form of surgery within five years.
This type of surgery (technically known as trabeculectomy) uses conventional surgical instruments to open a passage through the trabecular meshwork so that aqueous humor can drain into surrounding tissues. The operation takes about 20 minutes, is performed on an outpatient basis under local anesthesia, and is relatively safe and long lasting.
In general, a protective eye patch must be worn for one day after the procedure, and people are advised to avoid driving, bending over, and performing strenuous activity for at least a week. If necessary, the drainage flap created during the surgery can be loosened or tightened later on with a new laser procedure (called suture lysis) or with the use of special adjustable sutures.
After filtration surgery, about 50 percent of people no longer need glaucoma medication, 35 to 40 percent may still need some, and 10 to 15 percent will need more surgery, including repeated trabeculectomy, tube-shunt surgery, or cyclodestructive surgery. Filtration surgery carries a risk of infection and bleeding in the eye and requires a longer recovery period than laser trabecular surgery.
Approximately one third of individuals develop cataracts within five years of surgery. It's not clear whether the surgery itself causes the cataracts or whether they would have occurred anyway. However, the cataracts can be surgically removed when necessary.
Researchers are working to improve the effectiveness of filtration surgery. A promising approach is the use of antimetabolites (substances that block biological processes) such as mitomycin or 5-fluorouracil. Both mitomycin and 5-fluorouracil can be applied as a liquid during surgery; 5-fluorouracil can also be injected under the surface of the eye after surgery. These medications interfere with normal wound healing so that the openings created by the procedure do not close. Currently, these antimetabolites are used primarily in people who have had unsuccessful filtration surgery and in younger individuals who normally have strong wound-healing abilities.
When filtration surgery is not successful, one alternative is to drain the excess aqueous humor using a shunt made of plastic tubing. The shunt is implanted into the front chamber of the eye, and the aqueous humor drains onto a plate sewn onto the side of the eye. The tissues surrounding the eye then absorb the fluid from the plate.
After the tube shunt surgery, the need for eyedrops continues, more often than after trabeculectomy surgery, and sometimes for life. In addition, certain procedures must be performed in the doctor's office to regulate eye pressure through the shunt. Eye surgeons at the Johns Hopkins Wilmer Eye Institute use the Baerveldt and the Ahmed shunts.
This form of glaucoma surgery uses a laser to destroy the ciliary bodya part of the eye that surrounds the lens and produces aqueous humor. Recovery time depends on the type and extent of the surgery. The procedure does not require an incision, so people can return to their normal daily activities earlier than after filtration surgery. Cyclodestructive surgery is usually used only when other measures have failed.