Cataract is clouding of the lens inside the eye which leads to a decrease in vision. It is the most common cause of blindness and is conventionally treated with surgery. Visual loss occurs because opacification of the lens obstructs light from passing and being focused on to the retina at the back of the eye.
It is most commonly due to biological aging but there are a wide variety of other causes. Over time, yellow-brown pigment is deposited within the lens and this, together with disruption of the normal architecture of the lens fibers, leads to reduced transmission of light, which in turn leads to visual problems.
Those with cataracts commonly experience difficulty in appreciating colours and changes in contrast, driving, reading, recognising faces, and coping with glare from bright lights.
Signs and symptoms vary depending on the type of cataract, though there is considerable overlap. People with nuclear sclerotic or brunescent cataracts often notice a reduction of vision. Those with posterior supcapsular cataracts usually complain of glare as their major symptom.
The severity of cataract formation, assuming that no other eye disease is present, is judged primarily by visual acuity test. The appropriateness of surgery depends on a patient's particular functional and visual needs and other risk factors, all of which may vary widely.