Cataract

A cataract is a clouding of the eye's lens that blurs vision. As of 2020, it is the leading cause of blindness globally, with over 200 million people experiencing some degree of vision loss from it. While aging is the most common trigger, cataracts can also stem from eye injuries, radiation exposure, congenital conditions, or other diseases.

Symptoms vary based on the cataract's location and severity. Early on, mild clouding may cause no noticeable issues. As it progresses, vision can become blurry or double, colors may seem faded, and lights might appear with halos. Bright light can become bothersome, and seeing at night grows difficult. These problems can make driving, daily tasks, and staying independent harder, raising the risk of falls and depression.

The lens clouds when the eye's natural cleaning systems falter over time, largely due to oxidative stress and aging. Risk factors include diabetes, long-term corticosteroid use, obesity, other eye conditions, dietary deficiencies, smoking, heavy alcohol use, and prolonged sun exposure. Diagnosis involves an eye exam that tests vision at various distances, uses a slit lamp to inspect the lens, and may include a dilated retinal exam. The three main types are nuclear (center of the lens), cortical (outer edge), and posterior subcapsular (back of the lens).

As of 2025, no proven method exists to prevent or slow age-related cataracts, though controlling risks like smoking, alcohol, and UV exposure can help. Early symptoms may be managed with stronger glasses. When that fails, the only effective treatment is surgery to remove the cloudy lens and replace it with an artificial one, which generally improves quality of life. However, surgery is not widely available in many countries.

Globally, cataracts affect about 17.2% of people across all ages, with nuclear and cortical types being most common. Prevalence rises with age and is higher in women. Most people with cataracts live in lower-income countries; in South Asia, rates of cataract-induced blindness are especially high. In low- and middle-income regions, cataracts cause up to 50% of blindness, compared to roughly 5% in high-income countries.