THE EFFECT OF LONG-TERM MEDICAL THERAPY ON THE OUTCOME OF FILTRATION SURGERY

Long-term medical therapy and laser trabeculoplasty have been implicated as risk factors in the outcome of glaucoma filtration surgery. A retrospective analysis was performed of patients undergoing primary trabeculectomy during three key periods: before use of beta-blockers and laser trabeculoplasty (1975 and 1976), after introduction of beta-blocker therapy but before use of the laser (1980), and after common use of beta-blockers and laser (1985 and 1986). A total of 150 patients were included in the analysis. Eyes treated with laser trabeculoplasty at some time before filtration surgery had a decreased probability of successful filtration surgery (intraocular pressure less than 21 mm Hg, 75% vs 91% at one year, P = .05; 50% vs 86% at five years, P = .01). It is unknown whether laser was detrimental to subsequent filtration surgery or merely acted as a selection factor in identifying patients who would have less successful surgical outcomes. Preoperative use of topical medication did not influence the outcome of surgery. Patients having bilateral filtration surgery had similar outcomes between fellow eyes despite the longer use of therapy in the second eye (mean of 1.8 years between operations). In the subgroup of eyes with low preoperative intraocular pressures (less than 21 mm Hg), surgery was successful in reducing pressure to a lower level in 70% of eyes at one year (preoperative pressure, 17.8 mm; one-year postoperative pressure, 13.3 mm, P = .007).