Additive effect of dorzolamide: On aqueous humor flow in patients receiving long-term treatment with timolol

Objective: To determine the additive effect on aqueous humor flow of short-term dorzolamide treatment in patients with glaucoma receiving long-term treatment with timolol. Subjects and Methods: Thirty-nine patients with glaucoma, 19 at Mayo Clinic, Rochester, Minn, and 20 at the University of Uppsala, Uppsala, Sweden, who had been receiving timolol treatment in both eyes for at least 1 year were studied. Aqueous flow was measured with fluorophotometry and intraocular pressure with tonometry. The effect of dorzolamide was compared with placebo when added to the long-term treatment regimen with timolol. Results: Dorzolamide reduced aqueous humor flow by 24% +/- 11% (mean +/- SD). The intraocular pressure as compared with placebo in the US cohort was reduced by 10% +/- 6% and in the Swedish cohort by 18% +/- 9%. Conclusions: Dorzolamide, a carbonic anhydrase inhibitor, has addictive effects as an ocular hypotensive agent with timolol, a P-adrenergic antagonist, even though both drugs are suppressors of aqueous humor flow. Dorzolamide's effect on flow in these patients is the same as reported previously in normal subjects who are not taking a P-adrenergic antagonist.