The relationship between cataract, cell swelling and volume regulation.

The cause of cataracts is not known. Data from epidemiological and case-control studies have suggested various risk factors, among them; sunlight, diabetes, diarrhoea, oxidative stress, smoking and alcohol. Many reports in the literature suggest that the hydrated state of the lens is linked to cataract and recently direct evidence has emerged linking lens swelling to cataract. This review attempts to collate the various strands of evidence relating the hydrated state of the lens in cataract and to construct a common pathway for cataractogenesis. This common pathway involves lens swelling, membrane permeabilization, vacuole and cleft formation, disturbance to the intracellular environment, protein aggregation/modification and light scatter. This hypothesis gives rise to some testable predictions amongst which is that under certain conditions the lens axial diameter will increase raising the possibility that pre-cataractous changes could be detected (e.g., by ultrasound) and, with appropriate action, the cataract could be prevented or delayed. There are encouraging signs from animal studies that certain types of lens opacification can be delayed or prevented, lending credibility to the objective of cataract prevention in humans. Even a delay in the onset of cataract would have a huge global impact. The incidence of cataract correlates with poverty, poor diet and poor hygiene and the vast majority of cataract is found in developing countries. Economic factors and a lack of cataract surgeons in these countries mean that surgery is not the long-term answer. Prevention is the only realistic global approach. This review concludes that detection of pre-cataractous changes and cataract prevention are achievable objectives and funds should be directed towards their realization.