Abstract

Normal intraocular pressure (IOP) measurements have not been established in cetaceans other than saying that they are high compared to other species. We are interested in establishing the normal range for various cetacean species, identify which tonometer is best for these animals, and what physical body position allows the most accurate measurements. Rebound tonometry was used to measure IOP in Atlantic bottlenose (Tursiops truncatus, n = 16), Pacific bottlenose dolphins (Tursiops truncatus gilli, n = 14), one Atlantic-Pacific hybrid, harbor porpoise (Phocoena phocoena, n = 1), Beluga whales (Delphinapterus leucas, n = 2) and Pilot whales (Globicephala macrorhynchus, n = 2); either beached position, stationed on trainer's feet or at the edge of the pool resting on their cervical region. Seven Atlantic bottlenose dolphins had IOPs measured with tonometrist (JMF) in the water, using rebound tonometry, daily for 4–6 days with animals in natural horizontal position. Applanation tonometry was used to measure IOP in 4 Atlantic bottlenose dolphins. Average IOP in Atlantic bottlenose dolphins, stationed on trainer's feet, using rebound tonometry, was 40.43 mm Hg OD and 40.57 mm Hg OS. Average IOP in Atlantic bottlenose dolphins using applanation tonometry was 28.95 mm Hg OD and 29.64 mm Hg OS. Average IOP in Pacific bottlenose dolphins using rebound tonometry was 38.27 mm Hg OD and 36.5 mm Hg OS, also stationed on trainers' feet. Three Pacific bottlenose dolphins were in beached position, and average IOP was 57.67 mm Hg OD and 57.33 mm Hg OS. IOP in eleven animals, in beached position, averaged 62.8 mm Hg OD and 60.7 mm Hg OS. The harbor porpoise's IOP was 29 mm Hg OD and 31 mm Hg OS, in beached position. A Beluga whale calf's (5 months of age) IOP measured in beached position was 16 mm Hg OU; and a 10-year-old Beluga whale's IOP was 25 mm Hg OU, stationed at edge of pool. Average IOP in dolphins in natural horizontal position was 33.56 mm Hg OD and 33.32 mm Hg OS. The IOPs of cetaceans have been reported as very high without actually reporting measurements. Pacific bottlenose dolphin IOPs measured slightly lower than Atlantic bottlenose dolphins, but this could be due to small sample size. Beached position in dolphins does not appear to be representative of normal IOP and may be aberrantly high due to stress and bodyweight on the ventral aspect probably compressing the jugular veins and increasing IOP. Measurements taken in natural horizontal position appeared least stressful to the animals, and the values were most similar to other species' published data. The rebound tonometer was deemed instrument of choice for this species by the authors. Further work is required to validate these findings.

Acknowledgements

The authors would like to thank everyone at Theater of the Sea, Dolphin Quest, Dolphin Adventures, Vancouver Aquarium, Seaworld San Antonio and San Diego, and Dolphin Discovery for their hard work in acquiring this data.