Abstract
The cetacean eye has many unique structural features, including a Bowman's layer and a cornea that thins centrally to create a functional divergent lens.1 Bowman's layer is an acellular, disorganized collagen layer located between the corneal stroma and epithelial basement membrane that is not found in many mammalian species. It has been identified in humans, non-human primates, some terrestrial herbivores, pinnipeds, and cetaceans.2-5 This study describes noninflammatory histopathological features found in the anterior cornea of cetacean globes submitted to and archived at the Comparative Ocular Pathology Lab of Wisconsin (COPLOW) with an emphasis on alterations in Bowman's layer and the corneal epithelial basement membrane. There are 14 globes from 8 Delphinapterus leucas in the COPLOW collection. Six neonate globes are histologically normal. One adult globe is distorted by anterior uveitis; the remaining 7 globes from 5 adult D. leucas have variably thickened acellular layers between Bowman's layer and the anterior epithelium that stains strongly PAS positive, consistent with the basement membrane. Within the COPLOW archive, there was a similar mild peripheral thickening of the basement membrane in 2 globes from 1 Tursiops truncatus. These eyes were otherwise normal. In 4 D. leucas globes, 5 T. truncatus globes, and 1 globe from a Tursiops aduncus, there are variable defects in Bowman's layer. Occasionally there is pannus of fibrosis dissecting between Bowman's layer and the epithelial basement membrane extending from these defects. In humans, basement membrane thickening has been seen in conjunction with diabetes mellitus and as an age-related change.6,7 Defects in Bowman's layer are a hallmark sign of, but not exclusive to, keratoconus in humans.8,9
Acknowledgements
The authors wish to thank Drs. Judy St. Leger and Steve Osborn of the Sea World Adventure Parks for ocular submissions used in this project.
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