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

OBJECTIVE: To assess rebound tonometry intraocular pressure (IOP) in unsedated horses without and with auriculopalpebral (AP) nerve blocks. ANIMALS STUDIED: Twenty-two client- and twenty university-owned horses (84 total eyes) with unremarkable ophthalmic examinations were evaluated. PROCEDURE: One eye of each horse was chosen randomly, an AP block performed for that eye, and IOP measured in both eyes with a TonoVet((R)) . The process was repeated for the contralateral eye 72 hours 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. RESULTS: Overall, blocked eyes had an 0.8 mm Hg lower average IOP than unblocked eyes (P = .039). IOP for client-owned horses was on average 3.2 mm Hg lower than in UGA-owned horses (P = .025) and was more impacted by AP block (1.4 mm Hg 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). CONCLUSION: 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.