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OBJECTIVE: To evaluate the effect of topical administration of 2% dorzolamide hydrochloride or 2% dorzolamide hydrochloride-0.5% timolol maleate on intraocular pressure (IOP) in clinically normal horses. ANIMALS: Eighteen healthy adult horses without ocular abnormalities. PROCEDURE: The IOP was measured at five time points (7 a.m., 9 a.m., 11 a.m., 3 p.m., 7 p.m.) over 11 days. On days 1 and 2, baseline values were established. On days 3 through 5, horses received 2% dorzolamide HCI (group D, n = 9) or 2% dorzolamide HCl-0.5% timolol maleate (group DT, 9) in one randomly assigned eye every 24 hours immediately following each daily 7 a.m. IOP measurement. On days 6 through 9, each drug was given every 12 hours (7 a.m. and 7 p.m.) in the treated eye. Measurements on days 10 and 11 assessed return to baseline. Mixed linear regression models compared mean IOP difference for each drug at each time period. RESULTS: Mean IOP decreased significantly in all eyes during the two dose/day period, compared with the baseline, one dose/day, and follow-up periods. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of either drug every 24 hours for short-term treatment does not reduce IOP significantly. Administering either drug every 12 hours induced a significant reduction of IOP; however, controlling for all variables, the reduction was less than 2 mmHg.
Dr A.M. Willis, Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Ohio State University, Columbus 43210, OH, USA
2.16 Chiasma and retrochiasmal central nervous system (Part of: 2 Anatomical structures in glaucoma)