Use of Rebound Tonometry as a Diagnostic Tool to Diagnose Glaucoma in the Captive California Sea Lion

PURPOSE: One of the most common medical problems seen in the California sea lion (Zalophus californianus) is ocular disease. Glaucoma is a disease that has not been evaluated extensively in the sea lion. Observing clinical signs and measuring intraocular pressures (IOP) is critical for early diagnosis. The objective of this project is to measure IOP in clinically normal captive sea lions without ocular pathology to establish a normal range.

METHODS: The TonoVetwas selected to be used in the study. The TonoVet uses a new non-invasive, rebound method to estimate IOP. An electrical magnetic tonometer probe
comes into contact with and rebounds from the corneal surface to estimate an IOP. In order to record an accurate IOP, six measurements were taken and averaged resulting with the mean value. A complete ophthalmic examination has been performed on all sea lions by a veterinary ophthalmologist.

RESULTS: Currently, there are twenty sea lions in the study with no clinical ocular pathology. Overall mean in 39 healthy eyes was 32.8 mmHg with a SD +/- 3.2 at a 95% CI of 26.4 to 39.1.

CONCLUSION: We have established a normal baseline range for IOP values in captive sea lions without ocular pathology. This range is higher than the generally accepted range using other tonometers (e.g.,Tono-Pen Vet®). This is likely due to the increased thickness of the pinniped cornea as well as the different mechanism of the instrument itself. This range will provide a comparative measurement when evaluating a diseased eye. By measuring the IOP regularly in juvenile sea lions, veterinarians will be able to determine when IOP’s begin to change so that medical management can be started prior to loss of vision.