Objective To assess intraocular pressure (IOP) in conditioned equine athletes and document changes with exercise. A secondary objective was to assess associations between IOP and heart rate, as well as with other subjective physical parameters.

Sample Population Horses were evaluated during 50 mile endurance ride competitions. Data were collected on 69 horses during 5 different competitions at 3 different locations with 59 horses ridden once, 9 horses ridden in two competitions, and 1 horse ridden in three competitions for a total of 80 horse-ride combinations.

Procedures Intraocular pressure was measured using a TonoVet® tonometer in both eyes of each horse prior to, at two time points during, and immediately after endurance competitions. Heart rates and subjective veterinary scores were recorded on ride cards at each time point.

Results For horses with shorter finishing times (≤400 minutes), IOP decreased by at least 3.10.9 mmHg (least square mean estimateSEM) from baseline to the end of endurance exercise (P<0.007), though upward fluctuation was apparent during the ride. For horses with longer finishing times IOP did not change significantly from baseline to the end of exercise. Responses also differed between horses awarded “Best Condition” relative to other horses, whereby the latter, but not the former, showed an overall decrease in IOP by end of exercise relative to baseline (estimate decrease of 3.20.6 mmHg; P <0.001). There was no evidence for any association between IOP and heart rate, nor between IOP and subjective clinical scores.

Conclusions Intraocular pressure fluctuated in horses during endurance riding competitions.