Ocular findings and reference values for selected ophthalmic diagnostic tests in the macaroni penguin (Eudyptes chrysolophus) and southern rockhopper penguin (Eudyptes chrysocome)

Abstract

To describe ophthalmic examination findings and standard diagnostic test results in 2 penguin species. Macaroni & Southern Rockhopper Penguins. Complete ophthalmic examinations including Schirmer tear test (STT), modified phenol red thread test (PTT), tonometry, and echobiometry were performed on penguins housed at the Detroit Zoo. Mean and standard deviation of ophthalmic tests are reported and compared for significance using two sample t-tests with significance set at P<0.05. Correlations between variables were assessed using Pearson's correlation coefficient. Cataracts were the most common finding, present in 64% of Macaroni Penguins, and 68% of Rockhopper Penguins. There were anterior segment anomalies in all eyes with cataracts consistent with lens-induced uveitis. The mean modified PTT for the Macaronis was 24.7±6.37mm/15s and 25.1±7.07mm/15s in the Rockhoppers. The mean STT value for the Macaronis was 12.1±5.43mm/min and 11.0±3.96mm/min in the Rockhoppers. Mean intraocular pressure (IOP) for the Macaronis was 21.9±7.05mmHg measured by applanation tonometry and 29.1±7.16mmHg using rebound tonometry. The Rockhoppers had a mean IOP of 20.0±5.77mmHg and 24.1±5.09mmHg for applanation and rebound tonometry, respectively. In both populations, there was a significant difference in IOP measurement between the two instruments. In the Macaroni penguins, the presence of cataracts correlated significantly with increased age and lower IOP readings. Anterior chamber distance and axial globe length were significantly greater in males than in females in both penguin species.