Abstract: Eyes of five sperm whales (Physeter macrocephalus) were investigated macro- and microscopically. The general anatomy corresponded well with previous reports on other cetacean species, as well as previous reports on the sperm whale eye. The sperm whale eye does not differ in any great respect from other odontocete eyes, except for the obvious larger size. The most prominent structures were a very thick sclera encapsulating the bulbus, a large, vascularized rete ophthalmica surrounding the optic nerve, and a massive musculus retractor bulbi. Lack of ciliary muscles was also noted as well as the presence of a choroid tapetum and giant ganglion cells in the retina. It is suggested that the anatomy of the sclera, ophthalmic rete and retractor muscle is linked to the ability of cetaceans to protrude and retract their eyes. The eye is retracted into the orbit by the retractor muscle with the thick sclera providing a firm basis for attachment as well as protection from deformation. Space for the eye in the orbit is provided by drainage of the rete for blood. Protrusion could be facilitated by relaxation of the retractor and eyelid muscles and a refilling of the rete with blood.

Key Words: CETACEA; ODONTOCETES; VISION; RETRACTION; RETE OPHTHALMICA; RETRACTOR MUSCLE; EYE MUSCLES; PHYSETER

Document Type: Research article

Pages: 31-36

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