Morphology of the Normal eye of the California Sea Lion (Zalophus californianus) with Attention to Accommodation

Dick Dubielzig

Carmen Colitz

Judy St Leger

Pinniped Vision• Evolutionary offshoot of the carivora

– Holangiotic retina– Canine-like tapetum

• Adaptations for underwater vision– Relatively round lens

• Adaptations for vision out of water– Small pupillary aperture – Relatively flat corneal curvature

• Accommodation • Adaptations for vision in dim light at great depths

– Tapetum covers an extensive portion of the fundus– Mechanisms for pupil dilation

Size of the Eye

California Sea Lion4.94cm x 3.64 cm

Elephant Seal6.2cm x 4.46 cm

Adaptations for underwater vision - The round lens

Adaptations for vision out of water

Flattened corneal surface

Pinpoint pupil

Pinniped vision and AccommodationReview of the literature

• Schusterman et.al, Why Pinnipeds don’t echolocate J Accust Soc Am 2000– No echolocation

• Hanke et.al., Corneal topography, refractive state, and accomodation in Harbor Seals (Phaco vitulina) Vision Research 2006– Flattened corneal plateau– Myopia and astigmatism in air and emmotropia and no astigmatism in

water

• West et.al. (Murphy), A comparative study of the anatomy of the iris and ciliary body in aquatic mammals. Can J Zool 1991– Documents the arrangement and orientation of the iris and ciliary muscles

in pinnipeds

Morphologic Features

Morphologic Features

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Morphologic Features

Morphologic Features

Contact Between the Ciliary Pars Plicata and the Lens Capsule

Regulation of Pupil Size• Pupil size increases in water in dim light but not

on land (Schusterman)• Since the dilator muscle is rudimentary, might this

represent a forward movement of the lens in water?

http://www.ucsc.edu/oncampus/currents/97-08-18/seal.htm