Ocular biometry and pathology in captive and free-ranging southern white rhinoceros (Ceratotherium simum simum) and south-central black rhinoceros (Diceros bicornus minor) in South Africa

Abstract

ABSTRACT Title: Ocular biometry and pathology in captive and free-ranging southern white rhinoceros (Ceratotherium simum simum) and south-central black rhinoceros (Diceros bicornus minor) in South Africa. Background: The available literature describing rhinoceros’ ocular abnormalities is limited. This may stem from the rarity of the animals and limited baseline ocular data available. The purpose of the project is to add to current knowledge regarding the normal ocular population parameters and prevalence of ocular pathology in rhinoceroses. Methods: Seventy-three immobilised rhinos underwent ophthalmic examination while immobilised for general veterinary care and procedures. The ophthalmic examinations were performed by the author of the study, a registered veterinarian with the South African Veterinary Council (SAVC), and by a registered SAVC specialist veterinary ophthalmologist, when he was available. The ophthalmic examination included the Schirmer Tear Test (STT), intraocular pressure (IOP), slitlamp biomicroscopy, fluorescein staining, keratometry and ocular ultrasonography and biometry. Exploratory data analysis was performed to establish the baseline parameters with binomial exact methods used to establish 95% confidence intervals for the estimate of the means of normal ocular parameters. Results: Seventy-three animals were examined, 68 were white rhino and 5 were black. Twenty-four were male and 49 were female. Mean STT OD: 19.09 mm/min (95%CI: 17.48 – 20.69); mean STT OS: 17.64 mm/min (95% CI: 16.14 – 19.14); mean IOP OD: 41.12 mmHg (95% CI: 36.74 – 45.51); mean IOP OS: 42.66 mmHg (95% CI: 38.52 – 46.81). The most common ocular abnormalities were keratitis (23 animals, 31.51%), corneal scar (12 animals, 16.44%), cataract (11 animals, 15.07%), corneal ulcer (7 animals, 9.59%), pigmentary keratitis (3 animals, 4.11%), corneal foreign body, posterior synechiae and persistent pupillary membrane was present in two animals each (2.74%), follicular conjunctivitis (1 animal, 1.37%); 6 right eyes were fluorescein positive (8.2%) and 3 left eyes were fluorescein positive (4.1%). Mean AGL OD: 26.2 mm (95% CI: 2.57 – 2.66); mean AGL OS: 26.0 mm m (95% CI: 2.55 – 2.65); mean ACD OD: 2.7 mm (95% CI: 0.25 – 0.28); OS: 2.7 mm (95% CI: 0.25 – 0.28 OS); mean CLT OD: 6.5 mm (95% CI: 0.64 – 0.66); mean CLT OS: 6.4 mm (95% CI: 0.63 – 0.66); mean PSD OD: 16.3 mm (95% CI: 1.6 – 1.66); mean PSD OS: 1.62 (95% CI: 1.6 – 1.65). Conclusion: The findings regarding normal biometry will aid in future examinations of the species. The prevalence of ocular disease is high and has seemingly little impact on their natural life.