Morphology of the eye and surrounding structures of the bowhead whale, Balaena mysticetus

Observations were made on eyes from 46 bowhead whales, Balaena mysticetus, taken in the subsistence harvest near Barrow, Point Hope, Savoonga, and Kak tovik, Alaska. Data reported here include palpebral, eyeball, corneal, scle ral, pupillary, and lens dimensions. These quantitative data have allowed u s to compare structures relative to one another and sometimes to compare th em with similar structures in other species. We found, for example, that th e cornea is almost three times as thick at its periphery as at its center; that when the ratio of scleral thickness and eyeball size are compared, the ratio, in the bowhead whale, is twice that of any other cetacean for which data were available; and that the corneal and pupillary width to height ra tios indicate a less elongated cornea and pupil than has been reported in o ther cetaceans. We also found a strong correlation between body length and eyeball size indicating that within the species, unlike what is seen betwee n species, larger animals have larger eyes. Novel observations include the presence of three periorbital fatty layers, 112 ciliary processes, the pres ence of scleral canals, the absence of an obvious fovea or macular region i n the retina, a holangiotic pattern of fundic vessels, the presence of zonu lar fibers and a lens sheath, and the absence of arl obvious pupillary oper culum. Anatomical features like the wide angle of divergence and the palpeb ral dimensions suggest the absence of binocular vision while features like the size of the palpebral sac, abundant conjuctival fat, and the prominence of the retractor bulbi muscle suggest mechanisms for the protrusion and re traction of the eyeball.