Spherical aberration of the fish lens: interspecies variation and age

Summary Spherical aberration of the eyes of a spectrum of freshwater fishes was determined by photographing the refractive effects of excised crystalline lenses on multiple parallel split laser beams. In general, spherical aberration is minimized by the developmentally related variation in lens refractive index. However, spherical aberration is marked and non-monotonic in a non-visual species such as the bullhead. Furthermore, the size and variability of the aberration appears to be related to visual need as indicated by diet and feeding habits. For example, the lenses of predatory sight feeders such as the pike (Esox lucius) or rock bass (Ambloplites rupestris) are optically superior to that of an omnivorous feeder as the carp (Cyprinus carpio).The effect of age was tested by examining rock bass lenses from fish two to seven years of age. Lens quality, as indicated by the amount of change in posterior focal length for beams of varying eccentricity from the optic axis, is optimum in lenses from five year old fish. The significance of this variation in lens quality is uncertain and requires further study with greater attention to specimens of advanced age.