Use of Rebound Tonometry as a Diagnostic Tool to Diagnose Glaucoma in the Captive California Sea Lion
Abstract
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 TonoVet® (Webster Veterinary) was 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.
Acknowledgements
The authors would like to give a special thank you to Mississippi State University College of Veterinary Medicine for the instrumentation and initial funding of this Masters study and the Institute for Marine Mammal Studies of Gulfport for providing the startup venue and guidance for the project. Additional thanks to Webster Veterinary for helping to provide the tonometer probes. A note of appreciation is given to the members of my Masters committee: Dr. Skip Jack, Dr. Lora Ballweber and Dr. Carmen Colitz for their support and encouragement throughout this study. A special thanks to the trainers (Tim Hoffland, Marci Romagnoli, and Shannon Huyser) and Dr. Connie Chevis for having an open mind to train this behavior for the first time. This research would not be possible without the help and skills of all of the staff, doctors, trainers, and animals of the following places: in Florida (SeaWorld®, Miami Seaquarium®, Dolphin Research Center, Theater of the Sea, Dolphins Plus, and Gulf World Marine Park), in New York (New York Aquarium and Atlantis Marine World®), Institute for Marine Mammal Studies, Gulfport, MS, US Navy Marine Mammal Program, CA, SeaWorld®, San Antonio, SeaWorld®, CA, Six Flags® Great Adventure and Wild Safari, NJ, Six Flags® Discovery Kingdom, CA, Mystic Aquarium & Institute for Exploration, CT, MaritimeAquarium, CT, Audubon Zoo, Louisiana, New England Aquarium, MA, Atlantis,Paradise Island, BahamasTM, Dolphin Island, Dominican Republic, ZooMarine®, Italy, and Dolphin Discovery, Mexico.
References
1. Colitz C.M.H, M. Renner, T. Schmitt, L. Dalton, S. Osborne, B. Chittick, T. Reidarson, S.J. Dugan, and J. McBain. 2006. Incidence of lens disease in captive pinnipeds. Vet Ophthalmol 9(6): 423.
2. Gulland F.M.D., M. Haulena, and L. Dierauf. 2001. Seals and sea lions. In: L.A. Dierauf and F.M.D. Gulland (eds). CRC Handbook of Marine Mammal Medicine: Health, Disease, and Rehabilitation, 2nd ed., CRC Press Inc., Boca Raton, FL; Pp. 920-921.
3. Knollinger A., C. Noelle, P. Barrett, and P. Miller. 2005. Evaluation of a rebound tonometer for measuring intraocular pressure in dogs and horses. J Am Vet Assoc 227: 244-47.