Amphibious visual optics of the eyes of the double-crested cormorant (Phalacrocorax auritus) and the brown pelican (Pelecanus occidentalis)

The visual optics of the eyes of the brown pelican and the double-crested cormorant were studied with the aim of determining their suitability for vision in air and in water. Refractive state (in air and in water), chromatic aberation, and corneal radii of curvature were measured. Both species are approximately emmetropic in air. However, while the pelican cannot compensate for the refractive loss of the cornea in water the cormorant can. Chromatic aberration is insignificant in both species and can have little effect in reducing the hyperopia associated with movement to water. The corneas of neither species were excessively flattened. We believe that the cormorant compensates for the refractive change induced by movement from air to water by means of a very large accommodative ability.