A cataract is any opacity of the eye lens whether it is small and localised or a general loss of transparency. Cataracts may occur as a result of ageing or due to secondary factors including hereditary factors, trauma, inflammation, metabolic, nutritional disorders or radiation. Age-related cataracts are the most common. For a cataract to be deemed clinically significant it must cause a significant reduction in visual acuity or an impairment in function. In addition to age, other risk factors include diabetes, drugs eg corticosteroids, ultraviolet radiation, smoking, alcohol consumption and, although results are inconclusive, nutrition.