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Abstract

Short-wave absorbing compounds are common in the lenses of fish. Such pigments absorb radiation in the region of 300-500nm, restricting the passage of these wavelengths to the retina. The spectral transmission of lenses from 108 species of freshwater and marine fish from a total of 43 families was investigated here. A large number of fish had lens pigments with maximum absorbance around 320-330nm and/or 360nm, which were identified by HPLC and NMR as mycosporine-like amino acids; a group of low molecular weight, water soluble compounds. However, the short-wave absorbing pigment in the lens of the deep-sea species Stylephorus chordatus was isolated and identified as kynurenine, a tryptophan metabolite also found in the primate lens. A number of tropical freshwater species were also identified with high concentrations of another tryptophan derivative, 3-hydroxykynurenine, in the lens.

Variations in both lens pigment type and concentration were observed in several species and were found to be dependent on the age of the animal. A model was proposed to explain the changes occurring in lens transmission with age. An initial increase in pigment concentration produces a steep rise in the wavelength of lens 50% transmission which later levels off as pigment accumulation stops. The final stage is a drop in the 50% transmission wavelength, which occurs when pigment levels in the lens fall sharply as the lens continues to increase in volume.

Raising fish under high light, low light or UV conditions had no effect on either the lens pigmentation or the visual pigments, but did result in changes in both retinal structure and corneal pigmentation. This suggests that lens pigments do not accumulate in response to the environmental illumination.

Lenses of the frog, sheep, guinea pig, squirrel and 3 species of monkey were also found to contain a range of biochemically distinct short-wave absorbing compounds. Age- related changes were also observed in the macaque monkey lens. Three cephalopod species had lens pigments with similar short-wave absorbance to compounds in the fish lens, but HPLC analysis revealed that they are likely to be different.

Lens transmission measurements from a range of species support a role of fish lens pigments in increasing acuity. However, there is some evidence that short-wave absorbing compounds may also act to protect the retina from UV damage.

Publication Type:	Thesis (Doctoral)
Subjects:	R Medicine > RZ Other systems of medicine
Departments:	School of Health & Psychological Sciences > Optometry & Visual Sciences School of Health & Psychological Sciences > School of Health & Psychological Sciences Doctoral Theses Doctoral Theses

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