Effect of Topical 1% Cyclopentolate Hydrochloride on Tear Production, Intraocular Pressure, and Pupil Size in Healthy Turkman Horses.
Authors: Ansari Mood Maneli, Rajaei Seyed Mehdi, Faghihi Houman, Ghiadi Abdoljalil
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Cyclopentolone hydrochloride, an antimuscarinic agent commonly used for ophthalmic examination and refraction in horses, presents a favourable safety profile for cycloplegia when compared to atropine, though practitioners must remain alert to transient intraocular pressure elevation. Researchers administered a single topical drop of 1% cyclopentolate to one eye of 20 healthy Turkman horses whilst using the contralateral eye as control, then measured tear production (Schirmer tear test), intraocular pressure, and pupil diameter at intervals extending from 20 minutes to 120 hours post-instillation. Notably, tear production remained unaffected throughout the observation period; however, intraocular pressure increased significantly from 20 minutes and persisted elevated for over 90 minutes before declining below baseline at 120 minutes, whilst maximal pupil dilation of 15.8 ± 2.3 mm occurred at 12 hours post-treatment. For practitioners using this agent during diagnostic work or ophthalmic procedures, the extended cycloplegic effect (evidenced by sustained pupil dilation through 12 hours) makes it a practical alternative to atropine's variable absorption, though the early and sustained rise in intraocular pressure warrants caution in horses with pre-existing glaucoma or borderline ocular tension, and regular monitoring remains prudent in cases where eye health is compromised.
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Practical Takeaways
- •Cyclopentolate is a potent long-acting cycloplegic agent in horses; if used for ophthalmic examination or refraction, expect pupil dilation lasting at least 12 hours
- •Monitor IOP elevation in the 20-120 minute window post-instillation, particularly in horses with glaucoma risk; IOP normalizes after 120 minutes
- •Cyclopentolate does not affect tear production, making it safe for use in horses requiring tear film assessment
Key Findings
- •Topical 1% cyclopentolate caused significant IOP increase within 20 minutes, persisting beyond 90 minutes before declining below baseline at 120 minutes
- •Maximum vertical pupil dilation of 15.8 ± 2.3 mm occurred at 12 hours post-instillation in treated eyes
- •No significant effect on tear production (STT) was observed in either treated or untreated eyes over the entire measurement period
- •Cyclopentolate demonstrated prolonged cycloplegic effects in horses, suggesting potential as an alternative to atropine with fewer systemic side effects