Topical ropivacaine hydrochloride 0.5% and lidocaine hydrochloride 2% significantly reduce corneal sensitivity without short‐term negative side effects in horses

Abstract Objective To evaluate corneal sensitivity and acute side effects following application of ropivacaine hydrochloride 0.5% and lidocaine hydrochloride 2% on the healthy equine cornea. Animals Studied Eight healthy adult horses. Procedure A randomized, masked, crossover study design was utilized. Baseline Semiquantitative Preclinical Ocular Toxicology (SPOT) scores and corneal touch thresholds (CTT) using a Cochet‐Bonnet esthesiometer were recorded and measured, respectively, for eight healthy adult horses before medication application. Commercially available eyewash was used as a negative control. Ropivacaine hydrochloride 0.5% or lidocaine hydrochloride 2% solution was sprayed on a randomly selected eye, and the contralateral eye received eyewash. CTT was measured in both eyes at 1, 5, 15, 25, 35, 45, 55, 65, and 75 min post‐application. Post‐application SPOT scores were recorded immediately following the trial. Linear mixed model statistical analyses (mean ± standard error) were performed ( p < .05). Results Mean eyewash CTT (3.41 cm ± 0.464) was significantly different from ropivacaine‐treated (1.44 cm ± 0.562) ( p = .008) and lidocaine‐treated eyes (1.75 cm ± 0.562) ( p = .024); CTT was not significantly different between drug groups ( p = .88). Time to maximum anesthesia was not significantly different between ropivacaine (13.25 min ± 3.353) and lidocaine (16.25 min ± 3.353) ( p = .40). No side effects were appreciated as confirmed by SPOT. Conclusions Ropivacaine and lidocaine similarly decreased corneal sensitivity when applied topically without clinically evident short‐term ocular side effects. Lidocaine may be preferable in clinical settings due to its large, multi‐use vials and similar effects to ropivacaine.