Cataracts are a cloudy areas that form in the lens of the eye. The lens is normally clear. Poor vision results because the cloudiness interferes with light entering the eye. The opacities in the lens scatter the light, causing hazy vision, in the same way that a dirty window scatters light. Normal eye, with no cataract.
Light is focussed on the retina.
Eye with cataract. Light is scattered, causing blurred, hazy vision. Cataracts are due to a change in the lens material. However cataracts can become worse as more of the lens material changes. Most cataracts are a result of ageing and long-term exposure to ultraviolet light.