Environmental influence on shape of the crystalline lens: the amphibian example.

Amphibians are faced with the problem of adapting to aerial vision when undergoing metamorphosis. The rate and extent of ocular change has been examined in five species with widely varying life histories. Ocular effects and in particular lens shape changes were determined from measurements of gross anatomy at various metamorphic stages using a freeze-sectioning technique. In addition, refractive states were measured retinoscopically in air and water where possible. All larval animals have the ocular structure and optics typical of teleost fish. Adults show varying levels of adaptation to aerial vision, depending on the degree of departure from an aquatic style of behavior. In certain cases the spherical aquatic shape of the lens is maintained while in others, lens shape is altered markedly to a flattened elliptical form. Histological study indicates that change in lens shape is brought about by a rapid increase of mitotic activity of equatorial epithelial cells at critical periods during metamorphosis.