The world's leading cause of blindness is usually curable with surgery
Cataracts, a clouding of the eye's lens, leave around 12 to 15 million people blind worldwide and over 200 million with impaired sight. Replacing the cloudy lens with an artificial one restores vision, yet in poorer countries cataracts cause up to half of all blindness, compared with about 5 percent in wealthy ones.
The lens is made mostly of water and proteins called crystallins, kept transparent by nutrients and antioxidants from the fluid at the front of the eye. With age that supply system weakens and the lens makes fewer crystallins. Damaged proteins start clumping, while oxidation bends others out of shape, and gradually the lens turns cloudy. Faulty enzymes that fail to break down old proteins properly can speed the clumping.
Ageing is the main cause, but eye injuries, radiation, conditions present at birth and other illnesses can also produce cataracts. Recognised risk factors include diabetes, where excess sugar can lead to sorbitol building up in the lens, long-term steroid use, smoking, heavy drinking, prolonged sunlight exposure, obesity and some genetic disorders. Women are slightly more affected than men. As of 2025 no method has been shown to prevent or delay age-related cataracts; studies of supplements and diet have produced mixed results.
Doctors classify cataracts by where the clouding sits. Nuclear cataracts affect the centre of the lens and are sometimes described by tint, such as brownish. Cortical ones form in the outer layer, appearing as spots, streaks or spoke-like lines. Posterior subcapsular cataracts develop at the back, just under the lens capsule. Symptoms range from faded colours and glare to halos around lights, double vision in one eye and poor night vision, and mild clouding may cause no symptoms at all.
Poor sight has wider consequences, including more falls, less independence, difficulty driving and higher rates of depression. Glasses can help early on, but surgery is the only effective treatment once vision is seriously affected. Across all ages about 17.2 percent of people have cataracts, and South Asia has the highest rates of blindness from them, largely reflecting uneven access to operations.
Source: Cataract
