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A cataract is a cloudy area in the lens of the eye that impairs vision.[1][7] Cataracts often develop slowly and can affect one or both eyes.[1] Symptoms may include faded colors, blurry or double vision, halos around light, trouble with bright lights, and difficulty seeing at night.[1] This may result in difficulty driving, reading, and recognizing faces.[8] Poor vision caused by cataracts may also result in an increased risk of falling and depression.[2] In 2020 cataracts caused 39.6% of all cases of blindness and 28.3% of visual impairment worldwide. Cataracts remain the single most common cause of global blindness.[3]
Cataracts are most commonly due to aging but may also be due to trauma or radiation exposure, be present from birth or occur following eye surgery for other problems.[1][4] Risk factors include diabetes, longstanding use of corticosteroid medication, smoking tobacco, prolonged exposure to sunlight and alcohol.[1] In addition, poor nutrition, obesity, chronic kidney disease and autoimmune diseases have been recognized in various studies as contributing to the development of cataracts.[9] Cataract formation is primarily driven by oxidative stress, which damages lens proteins, leading to their aggregation and the accumulation of clumps of protein or yellow-brown pigment in the lens.[10] This reduces the transmission of light to the retina at the back of the eye, impairing vision. Additionally, alterations in the lens's metabolic processes, including imbalances in calcium and other ions, contribute to cataract development.[11][1] Diagnosis is typically through an eye examination,[1] with ophthalmoscopy and slit-lamp examination being the most effective methods. During ophthalmoscopy, the pupil is dilated, and the red reflex is examined for any opacities in the lens. Slit-lamp examination provides further details on the characteristics, location, and extent of the cataract.[12]
Wearing sunglasses with UV protection and a wide brimmed hat, eating leafy vegetables and fruits and avoiding smoking may reduce the risk of developing cataracts or slow the process.[1][13] Early on, the symptoms may be improved with glasses.[1] If this does not help, surgery to remove the cloudy lens and replace it with an artificial lens is the only effective treatment.[1] 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.[1][14][4][15]
About 20 million people worldwide are blind owing to cataracts.[4] They are the cause of approximately 5% of blindness in the United States and nearly 60% of blindness in parts of Africa and South America.[15] Blindness from cataracts occurs in 10 to 40 per 100,000 children in the developing world and 1 to 4 per 100,000 children in the developed world.[7] Cataracts become more common with age.[1] In the United States, cataracts occur in 68% of those over the age of 80 years.[16] They are more common in women and less common in Hispanic and Black people.[16]
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.[17]
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.[17] 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.[21]
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.[20]
Risk factors for developing cataracts include the following:[20][17]
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 leasing 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
Many factors contribute to the formation of cataracts, but aging and oxidative stress are the most common.[17] The eye's lens is mostly made of water and proteins called crystallins.[18] 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.[17] These changes cause the lens to become cloudy over time.[18]
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.[19]
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.[20]
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.[18][20] 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 [20]
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.[19]
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.[22]
Different types of cataracts
Posterior polar cataract of an 8-year-old boy in left eye
As of 2025, there is no proven way to prevent or delay the development of age-related cataracts.[18][23] 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.[17][21][23]
Cataracts are mainly treated with surgery, however prescription glasses or contacts lenses can be used to help manage early visual impairments.[21][18]
Cataract surgery, using a temporal-approach phacoemulsification probe (in right hand) and "chopper" (in left hand) being done under an operating microscope at the U.S. Navy Medical Center in Portsmouth, VirginiaSlit lamp photo of posterior capsular opacification visible a few months after implantation of intraocular lens, seen on retroillumination
Cataract surgery is considered an appropriate treatment for individuals whose cataracts have caused visual impairments that limit their ability to carry out daily activities.[18][17] 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.[18] The risks associated with cataract surgery have declined in recent years, meaning that the threshold for requiring surgery has also decreased.[17]
Measurements of the eyes are taken before surgery to choose the correct artificial lens.[20] Pre-surgery medical testing has shown no reduction in complications during surgery and are therefore not recommended by clinical guidelines.[18][21] Cataract surgery is usually done with only local anaesthesia and sedation, meaning that the person undergoing surgery is awake during the procedure, however their eye is numbed.[20]General anesthesia may be used for children or adults with intellectual and psychiatric disabilities or those who cannot lie still for long periods of time.[18] The goal of cataract surgery is to provide the individual with the best possible vision and it can improve both nearsighted and farsighted vision.[20]
Phacoemulsification is the most common and preferred method of cataract surgery. It uses ultrasound waves to break up the cloudy lens, which is then removed from the eye.[17] This procedure is usually performed as an outpatient surgery, meaning people can go home the same day as their surgery. Compared with manual extracapsular cataract extraction (ECCE) and manual small-incision cataract surgery (MSICS), phacoemulsification generally provides better uncorrected distance vision after surgery and has a lower risk of complications, such as the iris slipping through the incision or tearing of the back lens capsule.[21]
Phacoemulsification begins by making a small incision in the cornea and filling the front of the eye with a gel to protect its structures. A small circular opening is then made in the front of the lens capsule to access the cataract.[17] A handheld ultrasound probe breaks the cloudy lens into small pieces (phacoemulsification). These pieces are then gently suctioned out while keeping the lens capsule and its supporting fibers (zonules) intact. After the cataract is removed, a flexible artificial intraocular lens (IOL) is inserted through the small incision. The lens unfolds inside the remaining lens capsule, where it is held securely in the same position as the natural lens.[18] Finally, the small corneal incisions are sealed with water, and stitches are usually not needed.[17]
Small incision cataract surgery (SICS) is another common method of cataract removal. Unlike phacoemulsification, it uses a slightly larger incision in the white part of the eye (sclera) so the cloudy lens can be removed in one piece instead of being broken up with ultrasound. The remaining steps, including removing the leftover lens material and inserting an artificial intraocular lens, are similar to phacoemulsification.[17] SICS is used more in low- and middle-income countries because it is faster, requires less specialized equipment, and is less expensive.[17][21]
Slit lamp photo of anterior capsular opacification visible a few months after implantation of intraocular lens, magnified viewA South African woman experiences newfound eyesight after a patch was removed after surgery to remove an eye cataract.
Cataracts usually worsen with time, however the type of cataract, severity and how fast they progress varies by individual. When cataracts progress to the point of visual impairment, the only way of regaining vision is surgical treatment.[21] If there is no complication during or after cataract surgery, vision starts to improve within one to five days following surgery.[17]
The outcomes and individuals' level of satisfaction with cataract surgery are good.[18][21] A European study of cataract surgery outcomes performed in 2013, concluded that around 94% of those who have undergone surgery achieved a corrected distance visual acuity (CDVA) of 20/40 or better; 61.3% had a CDVA of 20/20 or better. Other studies have shown that 82-95% of those who had surgery achieved a CDVA of 20/40 or better.[21]
Serious complications during cataract surgery are uncommon. One of the main complications is a tear in the back of the lens capsule, which occurs in about 1–5% of surgeries and may allow the vitreous liquid inside the eye to move forward (vitreous prolapse). This can make it impossible to implant certain types of advanced artificial lenses and increases the risk of complications such as eye infection (endophthalmitis), swelling of the central retina (macular edema), and retinal detachment.[18]
The most common complication after cataract surgery is temporary macular edema, which causes blurred vision for several weeks or months. In most cases, the swelling improves on its own, but anti-inflammatory eye drops, including steroid and nonsteroidal anti-inflammatory (NSAID) drops, can help speed recovery.[18] Secondary cataracts can also develop after surgery.[17]
Age-related cataracts are responsible for 51% of world blindness, about 20 million people.[25] Globally, cataracts cause moderate to severe disability in 53.8million (2004), 52.2million of whom are in low and middle-income countries.[26]
In many countries, surgical services are inadequate, and cataracts remain the leading cause of blindness.[25] Even where surgical services are available, low vision associated with cataracts may still be prevalent as a result of long waits for, and barriers to, surgery, such as cost, lack of information, and transportation problems.[27]
In the United States, age-related lens changes have been reported in 42% between the ages of 52 and 64,[28] 60% between the ages 65 and 74,[29] and 91% between the ages of 75 and 85.[28] Cataracts affect nearly 22 million Americans age 40 and older. By age 80, more than half of all Americans have cataracts. Direct medical costs for cataract treatment are estimated at $6.8 billion annually.[30]
In the eastern Mediterranean region, cataracts are responsible for over 51% of blindness. Access to eye care in many countries in this region is limited.[31] Childhood-related cataracts are responsible for 5–20% of world childhood blindness.[32]
Vision loss due to cataracts increases the risk of dementia in the elderly population, increases the likelihood of falls and road traffic accidents, and by detrimental effects on the quality of life increases mortality.[33]
Cataract surgery was first described by the Ayurvedic physician, Suśruta (about 5th century BCE) in Sushruta Samhita in ancient India. Most of the methods focused on hygiene. Follow-up treatments include bandaging of the eye and covering the eye with warm butter.[34] Cataracts and their treatment in Ancient Rome are discussed in De Medicinae (29 CE) by the Latin encyclopedist Aulus Cornelius Celsus.[35] Archaeological evidence of eye surgery in the Roman era also exists.[36]
Galen of Pergamon (2nd century CE), the Greek physician, described an operation similar to modern cataract surgery. Using a needle-shaped instrument, Galen attempted to remove the cataract-affected lens of the eye.[37]
"Cataract" is derived from the Latincataracta, itself from the Ancient Greekκαταρράκτης (katarrhaktēs) 'waterfall'.[20][39] As rapidly running water turns white, so the term may have been used metaphorically to describe the similar appearance of mature ocular opacities. In Latin, cataracta had the alternative meaning "portcullis"[40] and the name possibly passed through French to form the English meaning "eye disease" (early 15th century), on the notion of "obstruction".[41] Early Persian physicians called the term nazul-i-ah, or "descent of the water"—vulgarised into waterfall disease or cataract—believing such blindness to be caused by an outpouring of corrupt humour into the eye.[42]
↑"Recognizing Cataracts". NIH News in Health. 2017-05-30. Retrieved 2020-02-02. Try wearing sunglasses or a hat with a brim. Researchers also believe that good nutrition can help reduce the risk of age-related cataract. They recommend eating plenty of green leafy vegetables, fruits, nuts, and other healthy foods.
12Sperduto RD, Seigel D (July 1980). "Senile lens and senile macular changes in a population-based sample". American Journal of Ophthalmology. 90 (1): 86–91. doi:10.1016/s0002-9394(14)75081-0. PMID7395962.
↑Kahn HA, Leibowitz HM, Ganley JP, Kini MM, Colton T, Nickerson RS, etal. (July 1977). "The Framingham Eye Study. I. Outline and major prevalence findings". American Journal of Epidemiology. 106 (1): 17–32. doi:10.1093/oxfordjournals.aje.a112428. PMID879158.
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Posterior polar cataract of an 8-year-old boy in left eye
Nuclear sclerosis cataract of a 70-year-old male
Cortical cataract of a 60-year-old male
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