Topical dorzolamide shows promise for macular edema

Topical dorzolamide (Trusopt, Merck) may offer hope for the treatment of macular edema in some patients with retinitis pigmentosa and X-linked retinoschisis. Rebound phenomenon after treatment needs to be addressed, Gerald Fishman, MD, reported.

Carbonic anhydrase inhibitors have been the treatment of choice for treating macular edema. However, the macular edema was seen to recur despite continued administration of those drugs and systemic effects were problematic, he explained. Dr. Fishman is professor of ophthalmology, Department of Ophthalmology and Visual Science, University of Illinois at Chicago.

Dorzolamide 2% was administered three times daily to 15 patients with retinitis pigmentosa. "There was an improvement in retinal thickness in at least one eye in 13 of the patients and in four of the patients in both eyes. There was an improvement in visual acuity of seven letters or more in at least one eye of seven patients," Dr. Fishman reported.

"Not all patients respond to the topical drugs," he pointed out. In addition, in some responders' rebound can occur after an initial improvement. Discontinuation of the drug for about 3 or 4 months resulted in another response.

When dorzolamide 2% was administered three times daily to patients with X-linked retinoschisis, the number of foveal cysts decreased. "Nine patients were given topical dorzolamide three times daily, and eight patients had a positive response. All had a one-line improvement in vision in at least one eye. Six patients had a sustained improvement,  two patients had a rebound effect, and one patient had no response," Dr. Fishman noted.

"Treatment of dorzolamide can improve cystoid macular edema in patients with retinitis pigmentosa and foveal cysts in X-linked retinoschisis. A rebound phenomenon can be observed with continued therapy. A sustained improvement can be observed in some patients for 2 years or more," he concluded. Dr. Fishman recommends starting patients with retinitis pigmentosa on a Diamox sequel (acetazolamide, Lederle Laboratories) 500 mg daily to determine the response of the macular edema with a switch to dorzolamide in the presence of intolerable side effects. Because of the marked response, he prefers to start patients with X-linked retinoschisis on dorzolamide 2% three times daily with monitoring for rebound.