Regeneration of the Lens in the Amphibian Eye

Abstract

Lens regeneration from the pupillary margin of the dorsal iris has been shown to occur in both larvae and adults of 13 spp. of the genus Triturus. The changes which take place during the process are the same in all spp. and involve depigmentation of the iris margin, formation of a lens vesicle, differentiation of primary and secondary lens fibers, and finally, detachment of the lens from the margin of the iris. The rate of regeneration is approx. the same for larvae of the same ages while adults ex hibit a slower rate. The ocular environment is best adapted for early stages of regeneration, however, "self-differentiation" in a foreign site can occur after the lens vesicle stage has been attained. Following lens extirpation, a single lens normally regenerates from the pupillary margin of the dorsal iris. How ever, regeneration of one or more lenses from the nasal or temporal parts can be brought about by subdividing the eye chamber. Regeneration of 2 lenses can also be brought about by inserting a piece of cornea or pliofilm horizontally through the dorsal iris. Rotation of the optic vesicle in the embryo indicates that the localization of competence for lens regeneration is fixed between stages 25 to 28 concomitantly with fixation of the mid-ventral location of the choroid fissure. If lens formation from the prospective lens ectoderm is prevented in an embryo, then a lens will develop from the dorsal iris, but not until after a delay of two weeks or more. From evidence now available, lens regeneration from the iris in many species of urodeles and in all anurans appears to be of questionable occurrence. It is concluded that the pigmented epithelium from the iris of some spp. of salamanders seems to possess a capacity for develop ing into a highly specialized tissue of an entirely different structural and functional nature, namely, a crystalline lens. This occurs in response to the removal of the lens and in the environment provided by the eye chamber.