Age-related
cataract (
ARC) is the leading cause of
blindness in the world, particularly in developing countries. In contrast,
cataract surgery has become the most frequent
surgical procedure in people aged 65 years or older in the Western world, causing a considerable financial burden to the health care system. The development of
cataracts is mainly an age-related phenomenon, although socioeconomic and lifestyle factors appear to influence their development, e.g. smoking has been found to directly influence
ARC. A key role in the pathomechanism of the crystalline lens alteration is played by
glucose metabolism and associated effected redox potential, which may induce oxidative damages.
Aldose reductase blockers were able to prevent the development of diabetic
cataracts in experimental studies, however clinical trials were interrupted due to unclear side effects. Other drugs with radical scavenging properties were effective in in vitro and in vivo experiments, but could not be proven to be efficient and safe in preclinical human trials. A number of epidemiological studies showed an increased risk of nuclear or cortical
cataract in people with low blood levels of
vitamin E. It is also known that the measured levels of
ascorbic acid decline with increasing age in the lens. Beta-Carotin and other non-polar
carotenoids seem to be missing and may therefore only play a minor role. Polarized
carotenoid lutein and
zeaxanthin are available in low concentrations and may therefore have some direct effects. The results of the present interventional studies are still controversial. While the Linxian studies indicated that the prevalence for nuclear
cataract was reduced by the supplementation with
retinol/
zinc or
vitamin C/
molybdenum, the AREDS trial showed no effect of the
antioxidant formulation on the development or progression of
ARC. Again, while the REACT study demonstrated a statistically significant positive treatment effect 2 years
after treatment for the US patients and for both subgroups (US & UK) after 3 years, no effect was observed in UK patients alone. In another US study, the Physician Health Study, no positive or negative effect of Beta-carotin was observed. Taken together, these studies suggest that any effect of
antioxidants on
cataract development is likely to be very small and probably is of no clinical or public health significance, thus removing a major rationale for 'anticataract'
vitamin supplementation among health-conscious individuals.