Cloudflare fetched the original article and streamed it through HTMLRewriter to apply an entirely new visual system without rebuilding the source page.
// request.cf · coarse context
A page that knows where it met you.
Only coarse request metadata is shown. This demo does not display or persist visitor IP addresses.
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]
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] 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]
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
The appropriateness of surgery depends on a person's functional and visual needs and other risk factors.[23] Cataract surgery can be performed whenever the cataract causes sufficient visual impairment or interferes with a person's daily activities; modern surgical techniques no longer require the cataract to become "mature" or "ripe" before removal.[24]
Surgery is usually outpatient and usually performed using local anesthesia. About 9 of 10 patients can achieve a corrected vision of 20/40 or better after surgery.[25]
Several recent evaluations found that cataract surgery can meet expectations only when significant functional impairment due to cataracts exists before surgery. Visual function estimates, such as VF-14, have been found to give more realistic estimates than visual acuity testing alone.[25][26] In some developed countries, a trend to overuse cataract surgery has been noted, which may lead to disappointing results.[27]
Phacoemulsification is the most widely used cataract surgery in the developed world.[28][29] This procedure uses ultrasonic energy to emulsify the cataract lens. Phacoemulsification typically comprises six steps:[30]
Anaesthetic – The eye is numbed with either a subtenon injection around the eye (see: retrobulbar block) or topical anesthetic eye drops. The former also provides paralysis of the eye muscles.
Corneal incision – Two cuts are made at the margin of the clear cornea to allow insertion of instruments into the eye.
Capsulorhexis – A needle or small pair of forceps is used to create a circular hole in the capsule in which the lens sits.
Phacoemulsification – A handheld ultrasonic probe is used to break up and emulsify the lens into liquid using the energy of ultrasound waves. The resulting 'emulsion' is sucked away.
Irrigation and aspiration – The cortex, which is the soft outer layer of the cataract, is aspirated or sucked away. Fluid removed is continually replaced with saline solution to prevent collapse of the anterior chamber (the front part of the eye).
Lens insertion – A plastic, foldable lens is inserted into the capsular bag that formerly contained the natural lens. Some surgeons also inject an antibiotic into the eye to reduce the risk of infection. The final step is to inject salt water into the corneal wounds to cause the area to swell and seal the incision.
A Cochrane review found little to no difference in visual acuity as a function of the size of incisions made for phacoemulsification in the range from ≤ 1.5mm to 3.0mm.[31] Extracapsular cataract extraction (ECCE) involves manually removing the lens, but leaving the majority of the capsule intact.[32] The lens is expressed through a 10- to 12-mm incision, which is closed with sutures at the end of surgery. ECCE is performed less frequently than phacoemulsification, but it can be useful for very hard cataracts or other situations where emulsification is problematic. Manual small-incision cataract surgery (MSICS) has evolved from ECCE. In MSICS, the lens is removed through a self-sealing scleral tunnel wound in the sclera, which, ideally, is watertight and does not require suturing. Although "small", the incision is still markedly larger than the portal in phacoemulsification. This surgery is increasingly popular in the developing world, where access to phacoemulsification is still limited.[citation needed]
Intracapsular cataract extraction (ICCE) is rarely performed.[33] Intracapsular cataract extraction (ICCE) involves removing the entire crystalline lens with its capsule through a large limbal incision. During lens expression, external pressure may be applied to the globe (typically at the limbus or sclera) to deliver the lens into the anterior chamber and out through the incision; alternatively, modern ICCE often uses cryoextraction, in which a cryoprobe adheres to the lens before removal. Because ICCE requires a large incision and removes the posterior capsule, it is associated with substantially higher risks of vitreous loss, retinal detachment, cystoid macular edema, and other complications than extracapsular cataract extraction or phacoemulsification, and is now rarely performed except in selected indications.[34]
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.
The postoperative recovery period (after removing the cataract) is usually short. The patient is usually ambulatory on the day of surgery, but is advised to move cautiously and avoid straining or heavy lifting for about a month. The eye is usually patched on the day of surgery, and the use of an eye shield at night is often suggested for several days after surgery.[23]
In all types of surgery, the cataractous lens is removed and replaced with an artificial lens, known as an intraocular lens, which stays in the eye permanently. Intraocular lenses are usually monofocal, correcting for either distance or near vision. Multifocal lenses may be implanted to improve near and distance vision simultaneously, but these lenses may increase the chance of unsatisfactory vision.[35]
Serious complications of cataract surgery include retinal detachment and endophthalmitis.[36] In both cases, patients notice a sudden decrease in vision. In endophthalmitis, patients often describe pain. Retinal detachment frequently presents with unilateral visual field defects, blurring of vision, flashes of light, or floating spots.[citation needed]
The risk of retinal detachment was estimated as about 0.4% within 5.5 years, corresponding to a 2.3-fold risk increase compared to the naturally expected incidence, with older studies reporting a substantially higher risk. The incidence is increasing over time in a somewhat linear manner, and the risk increase lasts for at least 20 years after the procedure. Particular risk factors are younger age, male sex, longer axial length, and complications during surgery. In the highest risk group of patients, the incidence of pseudophakic retinal detachment may be as high as 20%.[37]
The risk of endophthalmitis occurring after surgery is less than one in 1000.[38]
Corneal edema and cystoid macular edema are less serious but more common, and occur because of persistent swelling at the front of the eye in corneal edema or back of the eye in cystoid macular edema.[39] They are normally the result of excessive inflammation following surgery, and in both cases, patients may notice blurred, foggy vision. They normally improve with time and with the application of anti-inflammatory drops. The risk of either occurring is around one in 100. It is unclear whether NSAIDs or corticosteroids are superior at reducing postoperative inflammation.[40]
Posterior capsular opacification, also known as after-cataract, is a condition in which months or years after successful cataract surgery, vision deteriorates, or problems with glare and light scattering recur, usually due to thickening of the back or posterior capsule surrounding the implanted lens, so-called 'posterior lens capsule opacification'. Growth of natural lens cells remaining after the natural lens was removed may be the cause, and the younger the patient, the greater the chance of this occurring. Management involves cutting a small, circular area in the posterior capsule with targeted beams of energy from a laser, called Nd:YAG laser capsulotomy, after the type of laser used. The laser can be aimed very accurately, and the small part of the capsule that is cut falls harmlessly to the bottom of the inside of the eye. This procedure leaves sufficient capsule to hold the lens in place, but removes enough to allow light to pass directly through to the retina. Serious side effects are rare.[41] Posterior capsular opacification is common and occurs following up to one in four operations, but these rates are decreasing following the introduction of modern intraocular lenses together with a better understanding of the causes.[citation needed]
Age-related cataracts are responsible for 51% of world blindness, about 20 million people.[44] Globally, cataracts cause moderate to severe disability in 53.8million (2004), 52.2million of whom are in low and middle-income countries.[45]
In many countries, surgical services are inadequate, and cataracts remain the leading cause of blindness.[44] 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.[46]
In the United States, age-related lens changes have been reported in 42% between the ages of 52 and 64,[47] 60% between the ages 65 and 74,[48] and 91% between the ages of 75 and 85.[47] 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.[49]
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.[50] Childhood-related cataracts are responsible for 5–20% of world childhood blindness.[51]
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.[52]
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.[53] Cataracts and their treatment in Ancient Rome are discussed in De Medicinae (29 CE) by the Latin encyclopedist Aulus Cornelius Celsus.[54] Archaeological evidence of eye surgery in the Roman era also exists.[55]
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.[56]
"Cataract" is derived from the Latincataracta, itself from the Ancient Greekκαταρράκτης (katarrhaktēs) 'waterfall'.[20][58] 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"[59] and the name possibly passed through French to form the English meaning "eye disease" (early 15th century), on the notion of "obstruction".[60] 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.[61]
↑"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.
12Bollinger KE, Langston RH (March 2008). "What can patients expect from cataract surgery?". Cleveland Clinic Journal of Medicine. 75 (3): 193–96, 199–200. doi:10.3949/ccjm.75.3.193 (inactive 1 July 2025). PMID18383928. S2CID27022598.{{cite journal}}: CS1 maint: DOI inactive as of July 2025 (link)
↑Behndig A, Montan P, Stenevi U, Kugelberg M, Lundström M (August 2011). "One million cataract surgeries: Swedish National Cataract Register 1992–2009". Journal of Cataract and Refractive Surgery. 37 (8): 1539–1545. doi:10.1016/j.jcrs.2011.05.021. PMID21782099.
↑Gault J, Vander J (2015), Ophthalmology Secrets in Color, Elsevier Health Sciences, p.221, ISBN978-0-323-37802-4.
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.
_PHIL_4284_lores.jpg)
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
.jpg)
