Effect of topical 1% cyclopentolate hydrochloride on tear production, intraocular pressure, and pupil size in healthy horses.

This study was performed to evaluate the effect of topical 1% cyclopentolate hydrochloride on tear production (STT), intraocular pressure (IOP), and vertical pupil diameter (VPD) in healthy Turkman horses. Forty eyes of 20 clinically normal horses were used for this study, which were randomly assigned to two groups. Before instillation of 1% cyclopentolate, the baseline STT, IOP, and VPD of each group were recorded. Then, one drop of cyclopentolate was instilled randomly into one eye of each animal, and the contralateral eye served as control. Measurements were repeated at 20 minutes, 60 minutes, 90 minutes, 120 minutes, 12 hours, and 24 hours, and every 24 hours up to 120 hours post drug instillation in all animals. There was no significant effect on STT over the time course measured in both the treated and untreated eyes of the treatment groups after unilateral instillation of 1% cyclopentolate when compared to baseline values. A significant increase in the IOP was observed after 20 minutes, which persisted for more than 90 minutes; then, the IOP insignificantly decreased below the baseline values after 120 minutes. Maximum VPD was recognized at 12 hours post instillation in treated eyes (15.8 ± 2.3 mm), which was significantly different in comparison to the baseline (P = .07). Cyclopentolate could be considered as a long term and potent cycloplegic drug in horses when taking into account the possible side effect of atropine.