SELECTIVE LIGHT ABSORPTION BY THE LENSES OF LOWER VERTEBRATES, AND ITS INFLUENCE ON SPECTRAL SENSITIVITY

Abstract

A spectro-photometric technique was devised for measuring the spectral transmission of lenses from a variety of lower vertebrates. Lenses from frogs and a variety of fish, like the human lens, show a sharp cut-off of transmission near 400 mu, thus acting to filter out UV light to which retinal photopigments would otherwise be sensitive. Some fish lack such filters, and one shows a cut-off near 350 mu. Filtering lenses owe their property of selective absorption to a specific substance which was isolated and characterized as to ultra-violet absorption, solubility, and chromatographic behavior. Electrophysiological measurements of spectral sensitivity at short wave-lengths in frogs demonstrate that without the lens, scotopic sensitivity is in agreement with the absorption spectrum of rhodopsin down to 365 mu in the UV; normal animals are comparatively insensitive below 400 mu. The adaptive significance of such filtering lenses and the evolution of intra-ocular color filters in vertebrates is discussed.