C.J. Murphy1; T.D. Williams2; R.W. Bellhorn3;
M. Burns3; F. Schaeffel4; H.C. Howland4
Due to the otter's amphibious nature, the refractive contribution of the
cornea is routinely negated when the eve is submerged in water. To maintain acute vision in both
air and water would require the possession of an accommodative range that is equal to the
refractive contribution of the cornea in air. Using the techniques of static photorefraction and
dynamic photorefraction, we found the sea otter to be within a few diopters of emmetropia in
both air and water. Photokeratoscopy of live animals and geometric analysis of freshly
enucleated globes demonstrated the refractive contribution of the cornea in air (and hence the
otter's accomodative range) to be approximately 60 diopters (4X the range of a 10 year old
child. Morphologic examination revealed the otter eye to contain an extensive iridalsphincter
muscle and very well developed iridal dilator and meridional ciliary muscles. A similar muscular
arrangement has been described for amphibious birds in which iridal contraction plays an active
role in lenticular deformation. We suggest a similar mechanism is employed by the sea otter
eye.
Funded in part by the Veterinary Optometric Society.