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A cataract is a cloudy area in the
lens A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), ...
of the eye that leads to a decrease in vision. Cataracts often develop slowly and can affect one or both eyes. Symptoms may include faded colors, blurry or double vision, halos around light, trouble with bright lights, and trouble seeing at night. This may result in trouble driving, reading, or recognizing faces. Poor vision caused by cataracts may also result in an increased risk of
falling Falling or fallin' may refer to: *Falling (physics), movement due to gravity *Falling (accident) * Falling (execution) * Falling (sensation) People * Christine Falling (born 1963), American serial killer who murdered six children Books * ''Fa ...
and depression. Cataracts cause 51% of all cases of
blindness Visual impairment, also known as vision impairment, is a medical definition primarily measured based on an individual's better eye visual acuity; in the absence of treatment such as correctable eyewear, assistive devices, and medical treatment� ...
and 33% of visual impairment worldwide. Cataracts are most commonly due to
aging Ageing ( BE) or aging ( AE) is the process of becoming older. The term refers mainly to humans, many other animals, and fungi, whereas for example, bacteria, perennial plants and some simple animals are potentially biologically immortal. I ...
but may also occur due to
trauma Trauma most often refers to: *Major trauma, in physical medicine, severe physical injury caused by an external source *Psychological trauma, a type of damage to the psyche that occurs as a result of a severely distressing event *Traumatic inju ...
or radiation exposure, be present from birth, or occur following eye surgery for other problems. Risk factors include diabetes, longstanding use of
corticosteroid Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones. Two main classes of corticosteroids, glucocorticoids and mineralocorticoids, are involve ...
medication,
smoking tobacco Tobacco smoking is the practice of burning tobacco and ingesting the resulting smoke. The smoke may be inhaled, as is done with cigarettes, or simply released from the mouth, as is generally done with pipes and cigars. The practice is believed ...
, prolonged exposure to sunlight, and
alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...
. The underlying mechanism involves accumulation of clumps of protein or yellow-brown pigment in the lens that reduces transmission of light to the retina at the back of the eye. Diagnosis is by an
eye examination An eye examination is a series of tests performed to assess vision and ability to focus on and discern objects. It also includes other tests and examinations pertaining to the eyes. Eye examinations are primarily performed by an optometrist, op ...
. Prevention includes wearing
sunglasses Sunglasses or sun glasses (informally called shades or sunnies; more names below) are a form of protective eyewear designed primarily to prevent bright sunlight and high-energy visible light from damaging or discomforting the eyes. They can ...
and a wide brimmed hat, eating leafy vegetables and fruits, and avoiding smoking. 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. About 20 million people worldwide are blind due to cataracts. It is the cause of approximately 5% of blindness in the United States and nearly 60% of blindness in parts of Africa and South America. Blindness from cataracts occurs in about 10 to 40 per 100,000 children in the developing world, and 1 to 4 per 100,000 children in the developed world. Cataracts become more common with age. In the United States, cataracts occur in 68% of those over the age of 80 years. Additionally they are more common in women, and less common in Hispanic and Black people.


Signs and symptoms

Signs and symptoms vary depending on the type of cataract, though considerable overlap occurs. People with nuclear sclerotic or brunescent cataracts often notice a reduction of vision. Nuclear cataracts typically cause greater impairment of distance vision than of near vision. Those with posterior subcapsular cataracts usually complain of glare as their major symptom. The severity of cataract formation, assuming no other eye disease is present, is judged primarily by a visual acuity test. Other symptoms include frequent changes of glasses and colored halos due to hydration of lens.
Congenital cataract Congenital cataracts refers to a lens opacity which is present at birth. Congenital cataracts cover a broad spectrum of severity: whereas some lens opacities do not progress and are visually insignificant, others can produce profound visual impa ...
s can result in
amblyopia Amblyopia, also called lazy eye, is a disorder of sight in which the brain fails to fully process input from one eye and over time favors the other eye. It results in decreased vision in an eye that typically appears normal in other aspects. Amb ...
if not treated in a timely manner.


Causes


Age

Age is the most common cause of cataracts. Lens proteins denature and degrade over time, and this process is accelerated by diseases such as diabetes mellitus and hypertension. Environmental factors, including toxins, radiation, and ultraviolet light have cumulative effects which are worsened by the loss of protective and restorative mechanisms due to alterations in gene expression and chemical processes within the eye.
Oxidative stress Oxidative stress reflects an imbalance between the systemic manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage. Disturbances in the normal r ...
is an important pathogenic mechanism in cataract formation (seeHsueh YJ, Chen YN, Tsao YT, Cheng CM, Wu WC, Chen HC. The Pathomechanism, Antioxidant Biomarkers, and Treatment of Oxidative Stress-Related Eye Diseases. Int J Mol Sci. 2022 Jan 23;23(3):1255. doi: 10.3390/ijms23031255. PMID 35163178; PMCID: PMC8835903 for review). Senile cataracts are associated with a decrease in
antioxidant Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals. This can lead to polymerization and other chain reactions. They are frequently added to industrial products, such as fuels and lubricants, ...
capacity in the lens. An increase in oxidative stress in the lens or a decrease in the ability to remove reactive oxygen species can lead to the lens becoming more opaque.


Trauma

Blunt trauma causes swelling, thickening, and whitening of the lens fibers. While the swelling normally resolves with time, the white color may remain. In severe blunt trauma, or in injuries that penetrate the eye, the capsule in which the lens sits can be damaged. This damage allows fluid from other parts of the eye to rapidly enter the lens leading to swelling and then whitening, obstructing light from reaching the retina at the back of the eye. Cataracts may develop in 0.7 to 8.0% of cases following electrical injuries. Blunt trauma can also result in star- (stellate) or petal-shaped cataracts.


Radiation

Cataracts can arise as an effect of exposure to various types of radiation. X-rays, one form of ionizing radiation, may damage the DNA of lens cells. Ultraviolet light, specifically
UVB Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...
, has also been shown to cause cataracts, and some evidence indicates sunglasses worn at an early age can slow its development in later life.
Microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency rang ...
s, a type of nonionizing radiation, may cause harm by denaturing protective enzymes (e.g., glutathione peroxidase), by oxidizing protein thiol groups (causing protein aggregation), or by damaging lens cells via thermoelastic expansion. The protein coagulation caused by electric and heat injuries whitens the lens. This same process is what makes the clear albumen of an egg become white and opaque during cooking.


Genetics

The genetic component is strong in the development of cataracts, most commonly through mechanisms that protect and maintain the lens. The presence of cataracts in childhood or early life can occasionally be due to a particular syndrome. Examples of
chromosome abnormalities A chromosomal abnormality, chromosomal anomaly, chromosomal aberration, chromosomal mutation, or chromosomal disorder, is a missing, extra, or irregular portion of chromosomal DNA. These can occur in the form of numerical abnormalities, where ther ...
associated with cataracts include
1q21.1 deletion syndrome 1q21.1 deletion syndrome is a rare aberration of chromosome 1. A human cell has one pair of identical chromosomes on chromosome 1. With the 1q21.1 deletion syndrome, one chromosome of the pair is not complete, because a part of the sequence of the ...
,
cri-du-chat syndrome Cri du chat syndrome is a rare genetic disorder due to a partial chromosome deletion on chromosome 5. Its name is a French term ("cat-cry" or " call of the cat") referring to the characteristic cat-like cry of affected children. It was first d ...
,
Down syndrome Down syndrome or Down's syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is usually associated with physical growth delays, mild to moderate intellectual di ...
,
Patau's syndrome Patau syndrome is a syndrome caused by a chromosomal abnormality, in which some or all of the cells of the body contain extra genetic material from chromosome 13. The extra genetic material disrupts normal development, causing multiple and compl ...
, trisomy 18 ( Edward's syndrome), and Turner's syndrome, and in the case of
neurofibromatosis type 2 Neurofibromatosis type II (also known as MISME syndrome – multiple inherited schwannomas, meningiomas, and ependymomas) is a genetic condition that may be inherited or may arise spontaneously, and causes benign tumors of the brain, spinal cord, ...
, juvenile cataract on one or both sides may be noted. Examples of
single-gene disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosomal abnormality. Although polygenic disorders ...
include
Alport's syndrome Alport syndrome is a genetic disorder affecting around 1 in 5,000-10,000 children, characterized by glomerulonephritis, end-stage kidney disease, and hearing loss. Alport syndrome can also affect the eyes, though the changes do not usually affect v ...
, Conradi's syndrome,
cerebrotendineous xanthomatosis Cerebrotendinous xanthomatosis, also called cerebral cholesterosis, is an autosomal recessive form of xanthomatosis. It falls within a group of genetic disorders called the leukodystrophies. Presentation An inherited disorder associated with the ...
,
myotonic dystrophy Myotonic dystrophy (DM) is a type of muscular dystrophy, a group of genetic disorders that cause progressive muscle loss and weakness. In DM, muscles are often unable to relax after contraction. Other manifestations may include cataracts, int ...
, and
oculocerebrorenal syndrome Oculocerebrorenal syndrome (also called Lowe syndrome) is a rare X-linked recessive disorder characterized by congenital cataracts, hypotonia, intellectual disability, proximal tubular acidosis, aminoaciduria and low-molecular-weight proteinuria. ...
or Lowe syndrome.


Skin diseases

The skin and the lens have the same embryological origin and so can be affected by similar diseases. Those with
atopic dermatitis Atopic dermatitis (AD), also known as atopic eczema, is a long-term type of inflammation of the skin (dermatitis). It results in itchy, red, swollen, and cracked skin. Clear fluid may come from the affected areas, which often thickens over time ...
and
eczema Dermatitis is inflammation of the skin, typically characterized by itchiness, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened. The area of skin involved can ...
occasionally develop shield ulcer cataracts. Ichthyosis is an autosomal recessive disorder associated with cuneiform cataracts and nuclear sclerosis. Basal-cell nevus and
pemphigus Pemphigus ( or ) is a rare group of blistering autoimmune diseases that affect the skin and mucous membranes. The name is derived from the Greek root ''pemphix'', meaning "pustule". In pemphigus, autoantibodies form against desmoglein, whic ...
have similar associations.


Smoking and alcohol

Cigarette smoking Tobacco smoking is the practice of burning tobacco and ingesting the resulting smoke. The smoke may be inhaled, as is done with cigarettes, or simply released from the mouth, as is generally done with pipes and cigars. The practice is believe ...
has been shown to increase the risk of age-related cataract and nuclear cataract. Evidence is conflicting over the effect of alcohol. Some surveys have shown a link, but others which followed people over longer terms have not.


Inadequate vitamin C

Low vitamin C intake and serum levels have been associated with greater cataract rates. However, use of supplements of vitamin C has not demonstrated benefit.


Medications

Some medications, such as systemic, topical, or inhaled
corticosteroid Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones. Two main classes of corticosteroids, glucocorticoids and mineralocorticoids, are involve ...
s, may increase the risk of cataract development. Corticosteroids most commonly cause posterior subcapsular cataracts. People with schizophrenia often have risk factors for lens opacities (such as diabetes, hypertension, and poor nutrition). Second-generation
antipsychotic Antipsychotics, also known as neuroleptics, are a class of psychotropic medication primarily used to manage psychosis (including delusions, hallucinations, paranoia or disordered thought), principally in schizophrenia but also in a range of oth ...
medications are unlikely to contribute to cataract formation.
Miotics Miosis, or myosis (), is excessive constriction of the pupil.Farlex medical dictionary
citing: ...
and
triparanol Triparanol (, ; brand name and development code MER/29, as well as many other brand names) was the first synthetic cholesterol-lowering drug. It was patented in 1959 and introduced in the United States in 1960. The developmental code name of tri ...
may increase the risk.


Post-operative

Nearly every person who undergoes a
vitrectomy Vitrectomy is a surgery to remove some or all of the vitreous humor from the eye. Anterior vitrectomy entails removing small portions of the vitreous humor from the front structures of the eye—often because these are tangled in an intraocular l ...
—without ever having had cataract surgery—will experience progression of
nuclear sclerosis Nuclear sclerosis is an age-related change in the density of the crystalline lens nucleus that occurs in all older animals. It is caused by compression of older lens fibers in the nucleus by new fiber formation. The denser construction of the nuc ...
after the operation. This may be because the native vitreous humor is different from the solutions used to replace the vitreous (vitreous substitutes), such as BSS Plus. This may also be because the native vitreous humour contains
ascorbic acid Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits and vegetables, also sold as a dietary supplement and as a topical 'serum' ingredient to treat melasma (dark pigment spots) and ...
which helps neutralize oxidative damage to the lens and because conventional vitreous substitutes do not contain ascorbic acid. Accordingly, for phakic patients requiring a vitrectomy it is becoming increasingly common for ophthalmologists to offer the vitrectomy combined with prophylactic
cataract surgery Cataract surgery, also called lens replacement surgery, is the removal of the natural lens of the eye (also called "crystalline lens") that has developed an opacification, which is referred to as a cataract, and its replacement with an intraocul ...
to prevent cataract formation.


Other diseases

* Metabolic and nutritional diseases **
Aminoaciduria Aminoaciduria occurs when the urine contains abnormally high amounts of amino acids. In the healthy kidney, the glomeruli filter all amino acids out of the blood, and the renal tubules then reabsorb over 95% of the filtered amino acids back into ...
or Lowe's syndrome **
Cerebrotendineous xanthomatosis Cerebrotendinous xanthomatosis, also called cerebral cholesterosis, is an autosomal recessive form of xanthomatosis. It falls within a group of genetic disorders called the leukodystrophies. Presentation An inherited disorder associated with the ...
** Diabetes mellitus **
Fabry's disease Fabry disease, also known as Anderson–Fabry disease, is a rare genetic disease that can affect many parts of the body, including the kidneys, heart, and skin. Fabry disease is one of a group of conditions known as lysosomal storage diseases. ...
**
Galactosemia Galactosemia (British galactosaemia, from Greek γαλακτόζη + αίμα, meaning galactose + blood, accumulation of galactose in blood) is a rare genetic metabolic disorder that affects an individual's ability to metabolize the sugar galacto ...
/
galactosemic cataract A galactosemic cataract is cataract which is associated with the consequences of galactosemia. Types The presence of presenile cataract, noticeable in galactosemic infants as young as a few days old, is highly associated with two distinct types o ...
** Homocystinuria **
Hyperparathyroidism Hyperparathyroidism is an increase in parathyroid hormone (PTH) levels in the blood. This occurs from a disorder either within the parathyroid glands (primary hyperparathyroidism) or as response to external stimuli (secondary hyperparathyroidism) ...
**
Hypoparathyroidism Hypoparathyroidism is decreased function of the parathyroid glands with underproduction of parathyroid hormone (PTH). This can lead to low levels of calcium in the blood, often causing cramping and twitching of muscles or tetany (involuntary musc ...
** Hypervitaminosis D **
Hypothyroidism Hypothyroidism (also called ''underactive thyroid'', ''low thyroid'' or ''hypothyreosis'') is a disorder of the endocrine system in which the thyroid gland does not produce enough thyroid hormone. It can cause a number of symptoms, such as po ...
**
Hypocalcaemia Hypocalcemia is a medical condition characterized by low calcium levels in the blood serum. The normal range of blood calcium is typically between 2.1–2.6 mmol/L (8.8–10.7 mg/dL, 4.3–5.2 mEq/L) while levels less than 2.1 mmol ...
**
Mucopolysaccharidoses Mucopolysaccharidoses are a group of metabolic disorders caused by the absence or malfunctioning of lysosomal enzymes needed to break down molecules called glycosaminoglycans (GAGs). These long chains of sugar carbohydrates occur within the cells ...
** Wilson's disease *
Congenital A birth defect, also known as a congenital disorder, is an abnormal condition that is present at birth regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities can ...
**
Congenital syphilis Congenital syphilis is syphilis present ''in utero'' and at birth, and occurs when a child is born to a mother with syphilis. Untreated early syphilis infections results in a high risk of poor pregnancy outcomes, including saddle nose, lower extr ...
** Cytomegalic inclusion disease ** Rubella **
Cockayne syndrome Cockayne syndrome (CS), also called Neill-Dingwall syndrome, is a rare and fatal autosomal recessive neurodegenerative disorder characterized by growth failure, impaired development of the nervous system, abnormal sensitivity to sunlight ( photo ...
* Genetic syndromes **
Down syndrome Down syndrome or Down's syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is usually associated with physical growth delays, mild to moderate intellectual di ...
** Patau syndrome ** Edwards syndrome * Infections: **
Cysticercosis Cysticercosis is a tissue infection caused by the young form of the pork tapeworm. People may have few or no symptoms for years. In some cases, particularly in Asia, solid lumps of between one and two centimetres may develop under the skin. Aft ...
**
Leprosy Leprosy, also known as Hansen's disease (HD), is a long-term infection by the bacteria '' Mycobacterium leprae'' or '' Mycobacterium lepromatosis''. Infection can lead to damage of the nerves, respiratory tract, skin, and eyes. This nerve dam ...
** Onchocerciasis ** Toxoplasmosis ** Varicella * Secondary to other eye diseases: ** Retinopathy of prematurity **
Aniridia Aniridia is the absence of the iris, a muscular structure that opens and closes the pupil to allow light into the eye. It is also responsible for eye color. Without it, the central eye appears all black. It can be congenital, in which both eye ...
** Uveitis **
Retinal detachment Retinal detachment is a disorder of the eye in which the retina peels away from its underlying layer of support tissue. Initial detachment may be localized, but without rapid treatment the entire retina may detach, leading to vision loss and blin ...
** Retinitis pigmentosa


Diagnosis


Classification

Cataracts may be partial or complete, stationary or progressive, hard or soft. Histologically, the main types of age-related cataracts are nuclear sclerosis, cortical, and posterior subcapsular. Nuclear sclerosis is the most common type of cataract, and involves the central or 'nuclear' part of the lens. This eventually becomes hard, or 'sclerotic', due to condensation on the lens nucleus and the deposition of brown pigment within the lens. In its advanced stages, it is called a brunescent cataract. In early stages, an increase in sclerosis may cause an increase in refractive index of the lens. This causes a myopic shift (lenticular shift) that decreases hyperopia and enables presbyopic patients to see at near without reading glasses. This is only temporary and is called second sight. Cortical cataracts are due to the lens cortex (outer layer) becoming opaque. They occur when changes in the fluid contained in the periphery of the lens causes fissuring. When these cataracts are viewed through an
ophthalmoscope Ophthalmoscopy, also called funduscopy, is a test that allows a health professional to see inside the fundus of the eye and other structures using an ophthalmoscope (or funduscope). It is done as part of an eye examination and may be done as part ...
, or other magnification system, the appearance is similar to white spokes of a wheel. Symptoms often include problems with glare and light scatter at night. Posterior subcapsular cataracts are cloudy at the back of the lens adjacent to the capsule (or bag) in which the lens sits. Because light becomes more focused toward the back of the lens, they can cause disproportionate symptoms for their size. An immature cataract has some transparent protein, but with a mature cataract, all the lens protein is opaque. In a hypermature or Morgagnian cataract, the lens proteins have become liquid. Congenital cataract, which may be detected in adulthood, has a different classification and includes lamellar, polar, and sutural cataracts. Cataracts can be classified by using the lens opacities classification system LOCS III. In this system, cataracts are classified based on type as nuclear, cortical, or posterior. The cataracts are further classified based on severity on a scale from 1 to 5. The LOCS III system is highly reproducible.


Prevention

Risk factors such as UVB exposure and smoking can be addressed. Although no means of preventing cataracts has been scientifically proven, wearing
sunglasses Sunglasses or sun glasses (informally called shades or sunnies; more names below) are a form of protective eyewear designed primarily to prevent bright sunlight and high-energy visible light from damaging or discomforting the eyes. They can ...
that counteract ultraviolet light may slow their development. While adequate intake of vitamins A, C, and E may protect against the risk of cataracts,
clinical trial Clinical trials are prospective biomedical or behavioral research studies on human subject research, human participants designed to answer specific questions about biomedical or behavioral interventions, including new treatments (such as novel v ...
s have shown no benefit from supplements, although the evidence is mixed, but weakly positive, for a potential protective effect of the
carotenoid Carotenoids (), also called tetraterpenoids, are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, and fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips, ...
s,
lutein Lutein (;"Lutein"
zeaxanthin Zeaxanthin is one of the most common carotenoids in nature, and is used in the xanthophyll cycle. Synthesized in plants and some micro-organisms, it is the pigment that gives paprika (made from bell peppers), corn, saffron, goji ( wolfberries), ...
.


Treatment


Surgical

The appropriateness of surgery depends on a person's particular functional and visual needs and other risk factors. Cataract removal can be performed at any stage and no longer requires ripening of the lens. Surgery is usually "
outpatient A patient is any recipient of health care services that are performed by healthcare professionals. The patient is most often ill or injured and in need of treatment by a physician, nurse, optometrist, dentist, veterinarian, or other health care ...
" and usually performed using local anesthesia. About 9 of 10 patients can achieve a corrected vision of 20/40 or better after surgery. 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. In some developed countries, a trend to overuse cataract surgery has been noted, which may lead to disappointing results.
Phacoemulsification Phacoemulsification is a modern cataract surgery method in which the eye's internal lens is emulsified with an ultrasonic handpiece and aspirated from the eye. Aspirated fluids are replaced with irrigation of balanced salt solution to maintain t ...
is the most widely used cataract surgery in the developed world. This procedure uses ultrasonic energy to emulsify the cataract lens. Phacoemulsification typically comprises six steps: * Anaesthetic – The eye is numbed with either a subtenon injection around the eye (see:
retrobulbar block A retrobulbar block is a regional anesthetic nerve block in the retrobulbar space, the area located behind the globe of the eye. Injection of local anesthetic into this space constitutes the retrobulbar block. This injection provides akinesia of ...
) 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 Phacoemulsification is a modern cataract surgery method in which the eye's internal lens is emulsified with an ultrasonic handpiece and aspirated from the eye. Aspirated fluids are replaced with irrigation of balanced salt solution to maintain t ...
– 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 a saline solution to prevent collapse of the structure 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 Cochrane (previously known as the Cochrane Collaboration) is a British international charitable organisation formed to organise medical research findings to facilitate evidence-based choices about health interventions involving health professi ...
found little to no difference in visual acuity as a function of the size of incisions made for phacoemulsification in the range from ≤ 1.5 mm to 3.0 mm. Extracapsular cataract extraction (ECCE) consists of removing the lens manually, but leaving the majority of the capsule intact. The lens is expressed through a 10- to 12-mm incision which is closed with sutures at the end of surgery. ECCE is less frequently performed than phacoemulsification, but can be useful when dealing with 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 phacoemulsion. This surgery is increasingly popular in the developing world where access to phacoemulsification is still limited. Intracapsular cataract extraction (ICCE) is rarely performed. The lens and surrounding capsule are removed in one piece through a large incision while pressure is applied to the vitreous membrane. The surgery has a high rate of complications.


Prognosis


Postoperative care

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 use of an eye shield at night is often suggested for several days after surgery. In all types of surgery, the cataractous lens is removed and replaced with an artificial lens, known as an
intraocular lens Intraocular lens (IOL) is a lens implanted in the eye as part of a treatment for cataracts or myopia. If the natural lens is left in the eye, the IOL is known as phakic, otherwise it is a pseudophakic, or false lens. Such a lens is typically imp ...
, 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.


Complications

Serious complications of cataract surgery include
retinal detachment Retinal detachment is a disorder of the eye in which the retina peels away from its underlying layer of support tissue. Initial detachment may be localized, but without rapid treatment the entire retina may detach, leading to vision loss and blin ...
and
endophthalmitis Endophthalmitis is inflammation of the interior cavity of the eye, usually caused by infection. It is a possible complication of all intraocular surgeries, particularly cataract surgery, and can result in loss of vision or loss of the eye itself. ...
. In both cases, patients notice a sudden decrease in vision. In endophthalmitis, patients often describe pain. Retinal detachment frequently presents with unilateral
visual field The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments". Or simply, visual field can be defined as the entire area that can be seen when an eye is fixed straight at a point ...
defects, blurring of vision, flashes of light, or floating spots. 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 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%. The risk of endophthalmitis occurring after surgery is less than one in 1000. 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. 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 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. 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 which 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. 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. Vitreous touch syndrome is a possible complication of intracapsular cataract extraction.


Epidemiology

Age-related cataracts are responsible for 51% of world blindness, about 20 million people. Globally, cataracts cause moderate to severe disability in 53.8 million (2004), 52.2 million of whom are in low and middle income countries. In many countries, surgical services are inadequate, and cataracts remain the leading cause of blindness. 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. In the United States, age-related lens changes have been reported in 42% between the ages of 52 and 64, 60% between the ages 65 and 74, and 91% between the ages of 75 and 85. 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. 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. Childhood-related cataracts are responsible for 5–20% of world childhood blindness.


History

Cataract surgery was first described by the Ayurvedic physician,
Suśruta The ''Sushruta Samhita'' (सुश्रुतसंहिता, IAST: ''Suśrutasaṃhitā'', literally "Suśruta's Compendium") is an ancient Sanskrit text on medicine and surgery, and one of the most important such treatises on this subje ...
(about 5th century BCE) in '' Sushruta Samhita'' in
ancient India According to consensus in modern genetics, anatomically modern humans first arrived on the Indian subcontinent from Africa between 73,000 and 55,000 years ago. Quote: "Y-Chromosome and Mt-DNA data support the colonization of South Asia by m ...
. Most of the methods mentioned focus on hygiene. Follow-up treatments include bandaging of the eye and covering the eye with warm
butter Butter is a dairy product made from the fat and protein components of churned cream. It is a semi-solid emulsion at room temperature, consisting of approximately 80% butterfat. It is used at room temperature as a spread, melted as a condiment ...
. References to cataracts and their treatment in Ancient Rome are also found in 29 AD in ''De Medicinae'', the work of the Latin encyclopedist
Aulus Cornelius Celsus Aulus Cornelius Celsus ( 25 BC 50 AD) was a Roman encyclopaedist, known for his extant medical work, ''De Medicina'', which is believed to be the only surviving section of a much larger encyclopedia. The ''De Medicina'' is a primary source on d ...
. Archaeological evidence of eye surgery in the Roman era also exists. Galen of Pergamon (ca. 2nd century CE), a prominent Greek physician, surgeon and philosopher, performed an operation similar to modern cataract surgery. Using a needle-shaped instrument, Galen attempted to remove the cataract-affected lens of the eye. Muslim ophthalmologist Ammar Al-Mawsili, in his ''The Book of Choice in Ophthalmology'', written ''circa'' 1000 CE, wrote of his invention of a
syringe A syringe is a simple reciprocating pump consisting of a plunger (though in modern syringes, it is actually a piston) that fits tightly within a cylindrical tube called a barrel. The plunger can be linearly pulled and pushed along the inside ...
and the technique of cataract extraction while experimenting with it on a patient.


Etymology

"Cataract" is derived from the Latin ', meaning "waterfall", and from the Ancient Greek ('), "down-rushing", from καταράσσω (''katarassō'') meaning "to dash down" (from ''kata''-, "down"; ''arassein'', "to strike, dash"). 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" and the name possibly passed through French to form the English meaning "eye disease" (early 15th century), on the notion of "obstruction". 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.


Research

N-Acetylcarnosine drops have been investigated as a medical treatment for cataracts. The drops are believed to work by reducing oxidation and
glycation Glycation (sometimes called non-enzymatic glycosylation) is the covalent attachment of a sugar to a protein or lipid. Typical sugars that participate in glycation are glucose, fructose, and their derivatives. Glycation is the non-enzymatic proce ...
damage in the lens, particularly reducing
crystallin In anatomy, a crystallin is a water-soluble structural protein found in the lens and the cornea of the eye accounting for the transparency of the structure. It has also been identified in other places such as the heart, and in aggressive breast c ...
crosslinking. Some benefit has been shown in small manufacturer-sponsored randomized controlled trials but further independent corroboration is still required. Femtosecond laser mode-locking, used during cataract surgery, was originally used to cut accurate and predictable flaps in
LASIK LASIK or Lasik (''laser-assisted in situ keratomileusis''), commonly referred to as laser eye surgery or laser vision correction, is a type of refractive surgery for the correction of myopia, hyperopia, and an actual cure for astigmatism, sin ...
surgery, and has been introduced to cataract surgery. The incision at the junction of the sclera and cornea and the hole in capsule during capsulorhexis, traditionally made with a handheld blade, needle, and forceps, are dependent on skill and experience of the surgeon. Sophisticated three-dimensional images of the eyes can be used to guide lasers to make these incisions. A Nd:YAG laser can also then break up the cataract as in phacoemulsification.as PDF
The authors declare a financial interest in a company producing femtosecond laser equipment.
Stem cells have been used in a clinical trial for lens regeneration in twelve children under the age of two with cataracts present at birth. The children were followed for six months, so it is unknown what the long-term results will be, and it is unknown if this procedure would work in adults.


See also

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Galactosemic cataract A galactosemic cataract is cataract which is associated with the consequences of galactosemia. Types The presence of presenile cataract, noticeable in galactosemic infants as young as a few days old, is highly associated with two distinct types o ...
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Intraocular lens Intraocular lens (IOL) is a lens implanted in the eye as part of a treatment for cataracts or myopia. If the natural lens is left in the eye, the IOL is known as phakic, otherwise it is a pseudophakic, or false lens. Such a lens is typically imp ...


References


External links

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Pictures of different types of cataracts
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