Purpose: To compare the effectiveness of topical dorzolamide hydrochloride (Trusopt, Merck and Co., Inc., West Point, PA), a carbonic anhydrase inhibitor, with that of oral acetazolamide (Diamox; Lederle Laboratories, Pearl River, NY) for the management of chronic cystoid macular edema in patients with retinitis pigmentosa.
Methods: A prospective, double-masked, crossover study was conducted in five patients with retinitis pigmentosa who had chronic cystoid macular edema. After baseline visual acuity was measured and a fluorescein angiogram was obtained, each patient was randomly assigned to receive either topical dorzolamide or a placebo for 4 weeks, followed by a crossover for the same period. Oral acetazolamide then was given separately to each patient for 2 weeks. Each phase of the study was followed by a washout period of 4 weeks, during which the patient was taken off all medications. At each visit, best corrected visual acuity was measured, a fluorescein angiogram was obtained, a subjective assessment of the effects on visual function, and any side effects of the medication or placebo were recorded in the form of a questionnaire by an independent observer.
Results: Compared with baseline or placebo values, there was no measurable improvement in visual acuity on the Early Treatment Diabetic Retinopathy Study charts with dorzolamide in any of the patients. The visual acuity in three of five patients, however, improved by seven letters or more with acetazolamide. Compared again with baseline or placebo values, fluorescein angiograms of two of five patients showed improvement in macular edema in both eyes with the use of dorzolamide, whereas all five showed improvement with acetazolamide. The improvement in macular edema was more marked with acetazolamide than with dorzolamide. The effect of dorzolamide given three times a day was the same as that when it was given five times a day. One patient indicated that dorzolamide was more effective than acetazolamide in improving visual function, three of five patients believed that acetazolamide was more effective, and one felt that both were equally effective.
Conclusion: Dorzolamide provided improvement in cases of macular edema on fluorescein angiograms and subjective improvement of visual function in some patients with retinitis pigmentosa with cystoid macular edema. However, there was no measurable improvement in visual acuity with the topical use of this drug. Oral acetazolamide was found to be more effective than dorzolamide in managing macular edema and improving visual acuity.