Effect of auriculopalpebral nerve block on equine intraocular pressure measured by rebound tonometry (TonoVet® ).

Abstract

To assess rebound tonometry intraocular pressure (IOP) in unsedated horses without and with auriculopalpebral (AP) nerve blocks. Twenty-two client- and twenty university-owned horses (84 total eyes) with unremarkable ophthalmic examinations were evaluated. One eye of each horse was chosen randomly, an AP block performed for that eye, and IOP measured in both eyes with a TonoVet® . The process was repeated for the contralateral eye 72hours later under the same conditions as the initial measurements. Horses were unsedated for nerve blocks and tonometry. Linear mixed-effects models were used for comparisons with statistical significance threshold of 0.05. Overall, blocked eyes had an 0.8mmHg lower average IOP than unblocked eyes (P=.039). IOP for client-owned horses was on average 3.2mmHg lower than in UGA-owned horses (P=.025) and was more impacted by AP block (1.4mmHg lower average in client-owned blocked versus unblocked eyes (P=.006)). Block effectiveness was ranked on a subjective scale ("good", "poor", no block/control), and IOP was on average lower in eyes with a good block (P=.008). Although there were statistically significant differences in IOP between blocked and unblocked eyes, between client- and UGA-owned horses, and between eyes with good and poor AP blocks, these differences were not clinically significant. Thus, AP blocks remain a useful tool for evaluating equine ophthalmic health with minimal impact on IOP assessment.