Cataract

A cataract is a cloudy area in the lens of the eye that impairs vision. How fast a cataract develops depends on the type and one or both eyes may be affected by the condition. Symptoms may include faded colors, blurry or double vision, halos around light, trouble with bright lights, and difficulty seeing at night. This may result in difficulty driving, loss of independence, and decreased ability to perform everyday tasks. Poor vision caused by cataracts may also result in an increased risk of falling and depression.
Cataracts are most commonly due to aging but may also be caused by trauma to the eye, radiation exposure, conditions present from birth or complications from other conditions. Risk factors include diabetes, longstanding use of corticosteroid medication, obesity, other eye conditions, dietary deficiencies, smoking tobacco, prolonged exposure to sunlight and alcohol use. Cataract formation is primarily driven by oxidative stress and aging. Over time, the systems within the eye that keep the lens clear don't work as well, leading to the lens clouding. Diagnosis is typically made through an eye examination, including testing vision at various distances, slitlamp microscopy, and retinal examination. Slit-lamp examination provides further details on the characteristics, location, and extent of the cataract. An ophthalmoscope or a slit lamp with special lenses can be used to evaluate the retina. Sometimes the eye will be dilated before examination to give a better view of the retina. There are many types of cataracts, differentiated by where in the lens the clouding occurs. The three most common types of cataracts are nuclear, which affect the center of the lens, cortical which affect the outer part of the lens, and posterior subcapsular which develop at the back of the lens.
As of 2025, there is no proven way to prevent or delay the development of age-related cataracts. However, risk factors such as alcohol use, smoking, and ultraviolet exposure can be controlled. Early on, the symptoms may be improved with glasses. If this does not help, surgery to remove the cloudy lens and replace it with an artificial lens is the only effective treatment. Cataract surgery is not readily available in many countries, and surgery is needed only if the cataracts are causing problems and generally results in an improved quality of life.
As of 2020, around 12 to 15 million people worldwide are blind due to cataracts and over 200 million have some level of visual impairments due to the condition. Cataracts remain the single most common cause of blindness. The prevalence of cataracts across all ages is 17.2%, with the most common types being nuclear and cortical cataracts. Cataracts become more common with age and are more common in women. Most individuals with cataracts live in lower income countries, with South Asia having the highest rates of cataract induced blindness. Access to cataract surgery varies around the world and those in low- and middle-income countries have lower rates of surgical treatments. In these regions cataracts are responsible for up to 50% of blindness, compared with only about 5% in high-income countries.