A comparative study of betaxolol and dorzolamide effect on ocular circulation in normal-tension glaucoma patients

Objective: To determine whether dosages of a selective P-blocking agent (be taxolol) and a topical carbonic anhydrase inhibitor (dorzolamide), sufficie nt to significantly lower intraocular pressure (IOP), have similar or dispa rate impact on the retinal and retrobulbar circulation. Design: Counterbalanced crossover, with open-label use of medications. Participants Nine persons with normal-tension glaucoma (NTG), intervention: After a 3-week drug washout, NTG patients were studied after 1 month of treatment with either dorzolamide or betaxolol, with determinati ons of IOP and retinal and retrobulbar hemodynamics, Main Outcome Measures: At baseline and after treatment with each drug, reti nal arteriovenous passage time was determined by scanning laser ophthalmosc opy after fluorescein dye injection, and flow velocities in the central ret inal and ophthalmic arteries were measured with color Doppler ultrasonograp hy imaging. Results: Betaxolol and dorzolamide each lowered IOP significantly, with the se changes apparent and maximal after 2 weeks (each P < 0.05), In contrast, dorzolamide (but not betaxolol) accelerated arteriovenous passage of fluor escein dye in the inferior temporal quadrant of the retina (P < 0.05). Neit her drug affected arteriovenous passage in the superotemporal retina or any aspect of central retinal or ophthalmic artery flow velocity after either 2 or 4 weeks. Conclusions: Although both dorzolamide and betaxolol are effective ocular h ypotensive agents and their topical instillation leaves retrobulbar hemodyn amics unaltered, dorzolamide alone accelerates inferotemporal retinal dye t ransit. (C) 2000 by the American Academy of Ophthalmology.