Special features of the lens relative to the environment.

The lenses of certain shallow-swimming marine vertebrates contain near-UV absorbing pigments. These pigments minimize chromatic aberration and maximize contrast sensitivity. Such pigments are chemically similar to those found in diurnal terrestrial vertebrate (ie: gray squirrel) lenses. Deep-swimming marine vertebrate lenses generally lack these pigments, so they must utilize all light available for vision. Two near-UV absorbing pigments were observed in the lenses of assorted teleosts and elasmobranchs: pigment I absorbs maximally at 320, while pigment II does so at 360 nm. They are both dialyzable, water extractable compounds; and I is more polar than II. Studies of the properties of extracted and purified teleost lens pigment using absorption spectroscopy, HPLC, TLC, and mass spectrometry suggest that these pigments are kynurenines with differing side groups. The absorption spectrum of I resembles N-formyl kynurenine, while that of II resembles L-kynurenine. Preliminary assays of tryptophan pyrrolase (TP) in teleost lenses showed a much greater enzyme activity in shallow-swimmer's lenses. Light in the environment may stimulate lens pigment production. The use of short wavelength light cutoff filters may be useful in improving vision by minimizing light-scattering and fluorescence.