Abstracts: 2024 Annual Scientific Meeting of the International Equine Ophthalmology Consortium, Nashville, Tennessee, <scp>USA</scp> , June 13–15, 2024

Purpose:The aim of this study was to evaluate changes in refractive errors (RE) and anterior chamber depth (ACD) over time during the instillation of 1% atropine and 1% cyclopentolate in clinically normal horses.Methods: Twenty-eight eyes of 14 horses that are clinically healthy (seven stallions and seven mares) were used in this study.The animals were randomly assigned to two groups (treatment and control).Before instillation of 1% atropine and 1% cyclopentolate hydrochloride or placebo, baseline RE and ACD (T0) of each animal were recorded.Then single doses of 0.2 mL of 1% atropine and 1% cyclopentolate hydrochloride were instilled randomly into one eye of each horse in the treatment group.In both groups, single dose of 0.2 mL of artificial tears was instilled in one randomly selected eye of each horse.The measurements were repeated at 10 minutes (T1), 30 minutes (T2), 60 minutes (T3), 90 minutes (T4), and 120 minutes (T5) post instillation.Results: In the treatment groups, no statistically significant changes were observed in ACD or RE compared to the control group.However, in the cyclopentolate group, ACD increased significantly at 30 minutes, and in the atropine group, ACD decreased slightly at the same time.Conclusions: Topical application of cycloplegic eye drops in healthy horses results in small changes in the parameters of ACD and RE, regardless of refractive index.Due to the adverse effects of atropine drops on intestinal motility compared with cyclopentolate, cyclopentolate may be a recommended cycloplegic agent for diagnostic and therapeutic measures.None.