CORNEAL ANATOMY OF MARINE MAMMALS

The corneal anatomy of fin whales (Balaenoptera physalus), minke whale s (Balaenoptera acutorostrata), harp seals (Phoca groenlandica), ringe d seals (Phoca hispida), and bearded seals (Eriganthus barbatus) was e xamined to determine if marine mammals have evolved specialized cornea s for life in a marine habitat. One to seven eyes of each species were analyzed: paraffin sections stained with haematoxylin and eosin for l ight microscopy; and ultrathin sections for transmission electron micr oscopy. All corneas contain the five typical mammalian layers: epithel ium, Bowman's layer, stroma, Descemet's membrane, and endothelium. The corneas of these marine mammals are thicker than human corneas becaus e of a thicker stromal layer. The other layers are thinner than those found in humans, except for the epithelial layer in the bearded seal a nd the cetaceans where it may provide extra protection for the eye dur ing feeding behaviour. The epithelial cells in all corneas studied hav e an abundance of tonofilaments, which may strengthen the cells and di stribute force across the corneal surface. No special organization of collagen fibrils was found in the stroma that would offer protection f rom ultraviolet radiation or glare for pinnipeds when on ice. The thic kness of the sclera in the cetaceans may serve to hold the inner globe of the eye in an elliptical shape, while the thinning of the sclera i n the equatorial region in pinnipeds may flatten the eye in air to red uce aerial myopia.