TDK conference 2018

The main objective of our study was to compare the degree and duration of corneal anaesthesia of lidocaine, bupivacaine, and oxybuprocaine in horses with normal eyes.

In this prospective, randomized masked crossover study we compared the anaesthetic effect of three different drugs, that is either not commercially available in Hungary or have not been tested on equine corneas as they are intravenous injections. Another aim was to record any ocular side effect related to the anaesthetic administration.

Ten horses with healthy eyes between 5 and 18 years of age were included in the study. Corneal sensitivity was determined by measuring each eye’s corneal touch threshold (CTT) with a Cochet-Bonnet aesthesiometer. Each eye’s baseline CTT was recorded prior to anaesthetic instillation at 0 minutes and after 5 minutes and every 10 minutes thereafter for 90 minutes, in total 11-time points. Each subject was randomly assigned to receive one of three treatments. There was a 72-hour washout period. Every horse received all treatments. A Friedman test was used to compare CTT measurements among treatment groups at each time point.

Median baseline CTT of eyes was 47.5-50 mm which is similar to ones previously reported in the literature. The minimum of mean CTT was 17 mm with bupivacaine, 28.75 mm with lidocaine, and 30 mm with oxybuprocaine. All three drugs were effective, however corneal sensitivity was significantly reduced from baseline values after application of one drop of bupivacaine. Mean maximal anaesthetic effect occurred at 5 minutes and lasted for 30 mins in case of bupivacaine. There was no relevant difference between median CTT values for lidocaine and oxybuprocaine treated eyes. Mean CTT values of the right and left eyes did not differ significantly. None of the anaesthetics had any ocular side effects.

The data in this study demonstrated that all three anaesthetics provided clinically effective anaesthesia of the cornea and were well tolerated. However, it was significant in case of bupivacaine when median CTT values were compared to baseline. Ocular tolerance was good using either anaesthetic, so intravenous solutions for injections of lidocaine and bupivacaine can be safely used for topical anaesthesia in horses.