Summary
Refractive states of three species of penguins (Rockhopper, Gentoo and King) were measured in air and water. Little or no refractive error, with a trend toward slight myopia (less than two dioptres), was found in air in each case. Moderate hyperopia (8–13 dioptres) exists in water. The refractive findings of this study are similar to those of a preliminary study made with the Blackfoot penguin. The relatively small alteration of refractive state associated with the change from air to water (in contrast to an approximate change of 40 dioptres for the human eye) is attributed to the flattened shape of the cornea. The chromatic aberration measured in these species is insufficient to account for the hyperopia found underwater. The maximum reduction of hyperopia resulting from a monochromatic (blue, blue-green) aquatic habitat would only amount to two dioptres. It is speculated that the remaining hyperopia is nullified by an accommodative mechanism.
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This research was supported by a grant from the National Research Council of Canada. The authors are grateful for the cooperation of the Scottish National Zoological Park, Edinburgh. In particular, the authors would like to thank Mr. Kennedy for assistance in handling the penguins. The authors would like to acknowledge the original observation by Barbara Sivak concerning the flattened appearance of the penguin cornea.
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Sivak, J.G., Millodot, M. Optical performance of the penguin eye in air and water. J. Comp. Physiol. 119, 241–247 (1977). https://doi.org/10.1007/BF00656636
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DOI: https://doi.org/10.1007/BF00656636