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.
Signs and symptoms The signs and symptoms of cataracts differ according to which part of the lens is affected and the characteristics of how the lens in affected. If there is only mild clouding of the lens (lens opacity), cataracts may not have any symptoms.
As the condition worsens, symptoms begin to develop. Symptoms of cataracts include blurry vision, nearsightedness, astigmatism, difficulties with night vision, sensitivity to light, double vision in one eye, decreased contrast and color vision, visual distortions (halos) or loss of part of the visual field.
As visual impairments worsen, cataracts can affect a persons ability to carry out everyday tasks. Reduced functioning may also lead to mental health difficulties, reduced social functioning, and reduced life expectancy. Vision loss is also associated with reduced physical activity and independence. Impairments in vision increase the risk of falls which can be associated with injuries. A persons ability to drive can also be impacted by vision loss.
Causes A cataract is a clouding of the eye's natural lens that can be present at birth (congenital) or develop later in life (degenerative). It can affect one or both eyes and occurs because of pathophysiological changes in the lens. Although cataracts are most commonly caused by aging, they can also result from inherited genetic conditions, environmental factors, certain diseases, or the use of some medications.
Risk factors for developing cataracts include the following: Age: aging is the main risk factor for the development of cataracts Genetics: those with relatives who have cataracts, as well as individuals with specific genetic conditions are more likely to develop cataracts Ultraviolet (UV) radiation: longterm UV exposure from the sun can damage lens proteins leading to a higher risk of cataracts Smoking: toxins from cigarette smoke cause damage to the lens leading to an increased risk of cataracts Alcohol use: chronic alcohol use contributes to lens damage and has been associated with heightened cataract risk Diabetes: high blood sugar levels may lead to sorbitol building up in the lens leading to an increased risk of developing cataracts High blood pressure: associated with heightened risk of cataracts Obesity: metabolic and vascular complications of obesity puts an individual at a higher risk for cataracts Medications: chronic corticosteroid usage along with phenothiazine, antidepressants, miotics, and statins can increase the risk of cataracts Diseases: cataracts can develop as a result of other eye disorders such as chronic anterior uveitis, pseudoexfoliation syndrome, acute congestive angle-closure glaucoma, severe nearsightedness (high myopia) and some inherited disorders (Marfan syndrome, Down syndrome, myotonic dystrophy, Alport syndrome, retinitis pigmentosa, late-onset retinal dystrophy, or neurofibromatosis type 2) Eye injuries: injuries to the eye can cause cataracts directly after the trauma or years later Radiation: exposure to ionizing radiation damages the lens cells, raising the risk of developing cataracts Diet: deficiencies of antioxidants, minerals, and vitamins C and E can increase the risk of cataracts Gender: women have a slightly more elevated risk of cataracts than men Ethnicity: some ethnic populations have a higher prevalence of cataracts Pollution: environmental pollutants can heighten cataract risk Lifestyle: excessive exposure to heat and using certain electronics without eye protection can increase risk of cataracts
Mechanism Many factors contribute to the formation of cataracts, but aging and oxidative stress are the most common. The eye's lens is mostly made of water and proteins called crystallins. The lens stays clear by using nutrients and antioxidants supplied by the fluid in the front of the eye (aqueous humour). As people age, the systems that transport these nutrients and protect the lens become less effective. The lens also produces fewer crystallin proteins, which normally help keep it clear. As a result, damaged proteins begin to clump together, while oxidation causes proteins to fold incorrectly and lose their normal function. These changes cause the lens to become cloudy over time.
These changes can happen naturally as the lens ages, but genetic, developmental, or environmental factors can speed up the process or make it worse. Anything that disrupts the normal balance of the lens—such as changes in pH, nutrients, water, or mineral levels—can damage the lens further and increase the risk of developing cataracts.
Genetic mutations that affect the proteins in the lens or the genes that control normal lens function can increase the risk of cataracts. In healthy individuals, enzymes break down proteins in a regulated fashion. If these enzymes do not work properly, proteins can be broken down incorrectly and start to clump together. Protein clumps make the lens cloudy, contributing to the development of cataracts.
Diagnosis
The diagnosis of cataracts is made using symptoms reported by the affected individual and eye examinations. Eye examinations are performed by an ophthalmologist or optometrist and consist of testing vision at various distances (visual acuity test), slitlamp microscopy, and retinal examination. A slit-lamp examination allows doctors to view parts of the eye in a magnified, three-dimensional view. Using a thin beam of light, the cornea, iris, lens, and anterior chamber can be examined. This makes it easier to detect clouding or other changes in the lens that may indicate a cataract. A dilated eye examination involves using eye drops to widen (dilate) the pupils, allowing for a better view of the back of the eye (retina). Using an ophthalmoscope or a slit lamp with special lenses, a doctor can examine the retina and other internal eye structures. This exam helps identify any other conditions that may be causing vision problems, in addition to cataracts
Classification A cataract is any clouding of the eye's lens. There are three main types, based on where the clouding occurs in the lens. Nuclear cataracts affect the center (nucleus) of the lens. They are often described by their tint, such as opalescent or brunescent, or by how advanced they are, ranging from immature to mature or hypermature. Cortical cataracts affect the outer part (cortex) of the lens. They can appear in different patterns, such as small spots, streaks, spoke-like lines, circular areas, or fluid-filled cracks (waterclefts). Posterior subcapsular cataracts develop at the back of the lens, just beneath the lens capsule. They are caused by a buildup of abnormal (fibrotic or spherical) cells and are considered a specific type of cortical cataract.
Cataracts can also be classified by the age in which they are developed or the cause. Age-based classification includes congenital cataracts (present at birth), postnatal (developed in the first few years of life), juvenile (under the age of 30), and senile (associated with older age). Congenital cataracts are most commonly caused by hereditary and developmental disorders. Other causes include chromosomal disorders and metabolic conditions.
Prevention 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 UV exposure can be controlled. Antioxidant supplementation, dietary supplements, regular physical activity, and a healthy diet have all been proposed to help prevent cataracts, however studies have had mixed results on the benefits of these methods.
Treatment Cataracts are mainly treated with surgery, however prescription glasses or contacts lenses can be used to help manage early visual impairments.
Surgical
Cataract surgery is considered an appropriate treatment for individuals whose cataracts have caused visual impairments that limit their ability to carry out daily activities. Other factors that may lead to cataract surgery include correcting a large difference in vision between the two eyes after cataract surgery on the other eye and improving the ability to examine and treat retinal diseases by providing a clearer view of the back of the eye. The risks associated with cataract surgery have declined in recent years, meaning that the threshold for requiring surgery has also decreased.