Purpose: To study the intraocular pressure (IOP)-lowering effect of adding a third or a fourth antiglaucoma medication to preexisting antiglaucoma medical therapy, for a follow-up period of one year.
Patients and methods: The authors performed a retrospective, nonrandomized, noncomparative, interventional study including all patients seen by a single glaucoma specialist at the University of Florida Eye Clinic between January 1, 2000 and December 31, 2000, who had a third or a fourth antiglaucoma medication added to their existing regimen of two or three antiglaucoma medications, respectively. The main outcome measured was IOP at 2, 6, 9, and 12 months after addition of an antiglaucoma medication. "Efficacy" success was defined as a decrease in intraocular pressure of greater than or equal to 20% from baseline, without a change in the antiglaucoma medical therapy. Also, "safety outcome" was analyzed based on the need for surgical intervention and/or the occurrence of intolerable side effects to the antiglaucoma medications leading to discontinuation of their use.
Results: Sixty-seven patients had a third, and 29 patients had a fourth antiglaucoma medication added to their existing regimen. Analysis for a specific time point showed a success rate of 48% at 2 months (n = 65), 47% at 6 months (n = 47), and 41% at 1 year (n = 39) after addition of a third antiglaucoma medication and 59% at 2 months (n = 29), 45% at 6 months (n = 22), and 55% at 1 year (n = 20) after addition of a fourth antiglaucoma medication. By Kaplan-Meier analysis the cumulative probability of achieving efficacy success (> or = 20% IOP decrease from baseline) was 33% at 6 months and 23% at 1 year after adding a third medication (Group A), and 43% at 6 months and 18% at 1 year after adding a fourth medication (Group B). Combining both efficacy and safety outcomes decreased the cumulative probability of success to 27% and 14% in Group A, and 31% and 14% for Group B, at 6 months and 1 year respectively.
Conclusion: Addition of a third and fourth antiglaucoma medication produces a clinically significant reduction in IOP in about 40 to 60% of patients at any single time point. However, the cumulative probability of success including safety outcomes is relatively poor at 6 months and 1 year. This suggests that adding another antiglaucoma medication to a regimen of two or three medications frequently does not achieve a significant (> or = 20%) fall in IOP.