Effects of topical 1% cyclopentolate hydrochloride on quantitative pupillometry measurements, tear production and intraocular pressure in healthy horses.

Abstract

To evaluate the effect of topical cyclopentolate hydrochloride (CH) on quantitative pupillometric readings (PR), tear production (TP), and intraocular pressure (IOP) in healthy horses. Fourteen client-owned horses. In a two-phase design study, each animal received 1% CH ophthalmic solution in the left eye [treated] and 0.9% NaCl in the right eye [control] (0.2mL each). In the first phase (n=7), TP, IOP, and PR assessment was performed by Schirmer tear test I, rebound tonometry and static pupillometry, at 1, 8, 24, 48, 72, 96, 120, 148, 172, and 196-hours post-instillation. In the second phase (n=7), plateau mydriasis was evaluated by assessing PR hourly for 8hours post-instillation. For PR assessment, pupil area (PA), vertical diameter (VPD), and horizontal diameter (HPD) were recorded. All pupillometries were obtained in a room with fixed light intensity (45-60lux). Statistical analysis was performed by generalized estimating equations method for the effect on parameters over time. After topical CH, significant differences in pupil dilation were seen from 1 to 172hours for VPD and from 8 to 24hours for PA, without significant differences on HPD over time. In the second phase, plateau PA and VPD were reached at 3hours, while plateau HPD at 2hours. No significant effects were detected on TP and IOP in both eyes at any time, nor on PR of the nontreated eyes. Topical 1% cyclopentolate hydrochloride could be considered an effective and safe option when a mydriatic/cycloplegic drug is needed in horses.