 The sperm whale 's eye does not differ greatly from those of other toothed whales except in size . It is the largest among the toothed whales , weighing about 170 g . It is overall ellipsoid in shape , compressed along the visual axis , measuring about 7 × 7 × 3 cm . The cornea is elliptical and the lens is spherical . The sclera is very hard and thick , roughly 1 cm anteriorly and 3 cm posteriorly . There are no ciliary muscles . The choroid is very thick and contains a fibrous tapetum lucidum . Like other toothed whales , the sperm whale can retract and protrude its eyes thanks to a 2 @-@ cm @-@ thick retractor muscle attached around the eye at the equator . 
