Nutrients and degenerative eye diseases

Cataract (opacity of the lens) and age-related degeneration of the macula of the retina are very common causes of disability in old age, and people are living longer. It seems likely that both of these conditions result from gradual photo-oxidative damage. The proteins in cataractous lenses are oxidized and 50 per cent of the fatty acids in membranes of retinal photo-receptors are highly polyunsaturated. The eye normally has unusually high concentrations of vitamin C and zinc which could have protective functions against free radical damage. For cataracts five reported case-control studies are reviewed and two prospective studies one of which included a very large number of subjects. Vitamin intakes were estimated from dietary histories or blood levels. In five of the six studies in which vitamin C was measured it appeared to be protective and vitamin E and carotenoids appeared protective in 5/7 studies. Other descriptive epidemiological studies are going on, including one in the Blue Mountains near Sydney. It is concluded that controlled trials of antioxidant nutrients for cataract prevention are now warranted. As to age-related muscular degeneration (ARMD), severe vitamin E deficiency is known to cause (a different type of) retinal degeneration spontaneously in humans (with cystic fibrosis or abetalipoproteinaemia) and experimentally in animals. Only three human case-control studies of ARMD and diet have been reported thus far and no clear relationship with any particular nutrient has emerged yet. Supplements containing antioxidant vitamins and zinc are being advertised and used in the USA and elsewhere but this is ahead of the evidence. More observational studies are needed and the US National Eye Institute is planning a 10 year intervention study, known as AREDS (Age-Related Eye Disease Study).