Success rates for incisional glaucoma surgery depend on patient factors as discussed earlier, but are also affected by surgical techniques. The use of antimetabolites has significantly improved both the success rate and the survival rate of trabeculectomies. Two typesof antimetabolites are commonly used in glaucoma surgery. 5-Fluorouracil (5-FU) inhibits DNA replication but is reversible and may be used intraoperatively, as well as multiple times postoperatively. Mitomycin-C permanently binds DNA, and can only be used once with maximal effect after~5 min.
The Fluorouracil Filtering Surgery Study examined the success rates of trabeculectomies with and without the use of postoperative 5-FU. Success was defined as IOP ,21 mmHg with or without medications and no need for re-operation to control IOP. The 5 years success rate of trabeculectomies was 49% with 5-FU use, but only 26% without antimetabolite use (Fig. 1.1) (27). One of the major causes of failure in both groups was early postoperative wound leak (within 2 weeks of surgery). At 5 years, the success rate for the 5-FU group was 54% in eyes without a leak and 28% in those with a leak. The 5 year success rate in the group without antimetabolites was 24% without a wound leak and 15% with a leak (28). Risk factors for wound leaks include the use of antimetabolites, one-layer (vs. two-layer) conjunctiva-Tenon capsule closure, inferiorly located trabeculectomy, and older patients.
More recent studies have demonstrated similar efficacy with intraoperative mitomycin-C without the need for postoperative injections of antimetabolites (29). With the use of any antimetabolite, caution must be exercised as these patients may be more susceptible to complications from glaucoma surgery such as wound leaks or blebrelated infections
The decision to proceed with glaucoma surgery is usually straightforward: surgery is indicated when target pressures are not achieved or when optic disc and/or visual field loss occurs despite maximally tolerated medical and laser therapies. However, risk factors for progression other than IOP must be evaluated as well. The presence of numerous risk factors in addition to IOP suggests the need for more aggressive target pressures and treatment. Early surgery may be indicated when compliance with medical therapy is a problem, or in developing countries where the cost of medications may be prohibitive. Large diurnal pressure variations in a patient with severe disc damage may also be an indication for earlier surgery even if the mean IOP is at target. Conversely, quality of life issues should not be used in the decision to either proceed with or delay with surgery. Once the decision to proceed with surgery has been made, careful pre-operative evaluation must be performed to determine the optimal site and type of glaucoma surgery, including the use of antifibroblastic agents. This will help to improve the success of the surgery and minimize potential complications.
