Retinal abnormalities in experimental vitamin E deficiency.
Physiological and biochemical studies have been carried out longitudinally over a period of 12 months in vitamin E deficient and control rats to gain an understanding of the mechanism whereby vitamin E conserves normal retinal function. Electroretinographic studies indicated that the primary effect of vitamin E deficiency was on the photoreceptors. Ultrastructural studies, however, did not show any morphological changes to the photoreceptors which could explain receptor dysfunction. A 30-40% loss of vitamin A (retinol) was found to be associated with vitamin E deficiency. This could be corrected by repletion with vitamin E, but there was no associated improvement in visual function. An irreversible loss of the long-chain polyunsaturated fatty acids from the retina, increased lipid peroxidation and alterations in membrane fluidity were also detected during vitamin E deficiency. We suggest that a deficiency of vitamin E leads to changes in the membrane microenvironment, which could affect photo transduction by either impairing the ability of rhodopsin to undergo conformational changes to the active form, or by disrupting the hyperpolarising and depolarising processes of the photoreceptors.