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

Abstract

ObjectiveTo evaluate the effect of topical cyclopentolate hydrochloride (CH) on quantitative pupillometric readings (PR), tear production (TP), and intraocular pressure (IOP) in healthy horses.Animals studiedFourteen client‐owned horses.ProceduresIn 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] (0.2 mL 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 8 hours 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 (45‐60 lux). Statistical analysis was performed by generalized estimating equations method for the effect on parameters over time.ResultsAfter topical CH, significant differences in pupil dilation were seen from 1 to 172 hours for VPD and from 8 to 24 hours for PA, without significant differences on HPD over time. In the second phase, plateau PA and VPD were reached at 3 hours, while plateau HPD at 2 hours. No significant effects were detected on TP and IOP in both eyes at any time, nor on PR of the nontreated eyes.ConclusionsTopical 1% cyclopentolate hydrochloride could be considered an effective and safe option when a mydriatic/cycloplegic drug is needed in horses.

Effect of topical cyclopentolate alone or combined with phenylephrine in healthy horses

“…The mean value of the maximal vertical PD was 15.8 mm in the treated eye. This result was lower compared with Ortillés’ 9 and our study (18.6 and 20 mm respectively). This could be explained by the lower topical dose administered in Mood's study (single topical application of one drop of 1% cyclopentolate) compared with Ortillés' and our study (0.2 mL), and to the different pupil measurement techniques used.…”

“…In fact, the PD was calculated only 48 h after the last topical drug administration. A recent study showed a significant pupil dilation up to 172 h after a single topical administration of 0.2 mL of 1% cyclopentolate 9 . Therefore, to evaluate a potential prolonged mydriasis secondary to the phenylephrine combination, as previously reported in dogs and cats, 10,11 the PD should have been measured for at least 172 h after the last drug administration, and ideally until the PD reached the baseline value in both groups.…”

“…5,7 Therefore, the use of another mydriatic agent, cyclopentolate, should be considered. It has been reported that a single topical administration of cyclopentolate is able to achieve significant mydriasis, 3,8,9 without any effect on tear production. 8,9 After a single topical administration of 0.2 mL of 1% cyclopentolate, intraocular pressure (IOP) did not change 9 ; however, these results differ from a previous study which reported a significant increase in the IOP in Turkman horses after one drop of 1% cyclopentolate, although not clinically significant.…”

“…It has been reported that a single topical administration of cyclopentolate is able to achieve significant mydriasis, 3,8,9 without any effect on tear production. 8,9 After a single topical administration of 0.2 mL of 1% cyclopentolate, intraocular pressure (IOP) did not change 9 ; however, these results differ from a previous study which reported a significant increase in the IOP in Turkman horses after one drop of 1% cyclopentolate, although not clinically significant. 8 To the authors' knowledge, no study evaluates the effect of repeated topical administration of cyclopentolate, which represents the usual clinical therapy.…”

Safety and efficacy of unilateral topical application of rocuronium bromide in healthy scops owls (Otus scops)

“…Pupillometry can be performed with a manual gauge, 11,13‐15 DSLR camera, and posterior image processor software, 16,19 infrared digital cameras with posterior image analysis, 17,20 or commercially available automated digital pupillometers 18 . Human medical studies have shown that manual pupillary assessment is subjected to significant inaccuracies and inconsistencies, 21,22 with interexaminer disagreement as high as 39% 23 .…”