Cataract
Overview
 
A cataract is a clouding that develops in the crystalline lens
Lens (anatomy)
The crystalline lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a...

 of the eye
Eye
Eyes are organs that detect light and convert it into electro-chemical impulses in neurons. The simplest photoreceptors in conscious vision connect light to movement...

 or in its envelope, varying in degree from slight to complete opacity
Opacity (optics)
Opacity is the measure of impenetrability to electromagnetic or other kinds of radiation, especially visible light. In radiative transfer, it describes the absorption and scattering of radiation in a medium, such as a plasma, dielectric, shielding material, glass, etc...

 and obstructing the passage of light. Early in the development of age-related cataract, the power of the lens may be increased, causing near-sightedness (myopia
Myopia
Myopia , "shortsightedness" ) is a refractive defect of the eye in which collimated light produces image focus in front of the retina under conditions of accommodation. In simpler terms, myopia is a condition of the eye where the light that comes in does not directly focus on the retina but in...

), and the gradual yellowing and opacification of the lens may reduce the perception of blue colours. Cataracts typically progress slowly to cause vision loss
Vision loss
Vision loss or visual loss is the absence of vision where it existed before, which can happen either acutely or chronically .-Ranges of vision loss:...

, and are potentially blinding
Blindness
Blindness is the condition of lacking visual perception due to physiological or neurological factors.Various scales have been developed to describe the extent of vision loss and define blindness...

 if untreated.
Encyclopedia
A cataract is a clouding that develops in the crystalline lens
Lens (anatomy)
The crystalline lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a...

 of the eye
Eye
Eyes are organs that detect light and convert it into electro-chemical impulses in neurons. The simplest photoreceptors in conscious vision connect light to movement...

 or in its envelope, varying in degree from slight to complete opacity
Opacity (optics)
Opacity is the measure of impenetrability to electromagnetic or other kinds of radiation, especially visible light. In radiative transfer, it describes the absorption and scattering of radiation in a medium, such as a plasma, dielectric, shielding material, glass, etc...

 and obstructing the passage of light. Early in the development of age-related cataract, the power of the lens may be increased, causing near-sightedness (myopia
Myopia
Myopia , "shortsightedness" ) is a refractive defect of the eye in which collimated light produces image focus in front of the retina under conditions of accommodation. In simpler terms, myopia is a condition of the eye where the light that comes in does not directly focus on the retina but in...

), and the gradual yellowing and opacification of the lens may reduce the perception of blue colours. Cataracts typically progress slowly to cause vision loss
Vision loss
Vision loss or visual loss is the absence of vision where it existed before, which can happen either acutely or chronically .-Ranges of vision loss:...

, and are potentially blinding
Blindness
Blindness is the condition of lacking visual perception due to physiological or neurological factors.Various scales have been developed to describe the extent of vision loss and define blindness...

 if untreated. The condition usually affects both eyes, but almost always one eye is affected earlier than the other.

A senile cataract, occurring in the elderly, is characterized by an initial opacity in the lens, subsequent swelling of the lens and final shrinkage with complete loss of transparency. Moreover, with time the cataract cortex liquefies to form a milky white fluid in a Morgagnian cataract, which can cause severe inflammation if the lens capsule ruptures and leaks. Untreated, the cataract can cause phacomorphic glaucoma
Glaucoma
Glaucoma is an eye disorder in which the optic nerve suffers damage, permanently damaging vision in the affected eye and progressing to complete blindness if untreated. It is often, but not always, associated with increased pressure of the fluid in the eye...

. Very advanced cataracts with weak zonules are liable to dislocation anteriorly or posteriorly. Such spontaneous posterior dislocations (akin to the historical surgical procedure of couching
Couching (ophthalmology)
Couching is the earliest documented form of cataract surgery. As a cataract is a clouding in the lens of the eye, couching is a technique of dislodging the lens, thus removing the opacity...

) in ancient times were regarded as a blessing from the heavens, because some perception of light was restored in the cataractous patients.

Some children develop cataracts, called congenital cataracts, before or just after birth, but these are usually dealt with in a different way to cataracts in adults.

Cataract derives from the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 cataracta meaning "waterfall" and that from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 καταράκτης (kataraktēs) or καταρράκτης (katarrhaktēs), "down-rushing", from καταράσσω (katarassō) meaning "to dash down" (from kata-, "down"; arassein, "to strike, dash"). As rapidly running water turns white, the term may later have been used metaphorically to describe the similar appearance of mature ocular opacities. In Latin, cataracta had the alternate meaning "portcullis
Portcullis
A portcullis is a latticed grille made of wood, metal, fibreglass or a combination of the three. Portcullises fortified the entrances to many medieval castles, acting as a last line of defence during time of attack or siege...

" and it is possible that the name passed through French to form the English meaning "eye disease" (early 15c.), 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.

Epidemiology

Age-related cataract is responsible for 48% of world blindness, which represents about 18 million people, according to the World Health Organization (WHO). In many countries, surgical services are inadequate, and cataracts remain the leading cause of blindness. As populations age, the number of people with cataracts is growing. Cataracts are also an important cause of low vision in both developed and developing countries. Even where surgical services are available, low vision associated with cataracts may still be prevalent, as a result of long waits for operations and barriers to surgical uptake, such as cost, lack of information and transportation problems.

In the United States, age-related lenticular changes have been reported in 42% of those between the ages of 52 and 64, 60% of those between the ages 65 and 74, and 91% of those between the ages of 75 and 85.

The increase in ultraviolet radiation resulting from depletion of the ozone layer
Ozone depletion
Ozone depletion describes two distinct but related phenomena observed since the late 1970s: a steady decline of about 4% per decade in the total volume of ozone in Earth's stratosphere , and a much larger springtime decrease in stratospheric ozone over Earth's polar regions. The latter phenomenon...

 is expected to increase the incidence of cataracts.

History

The earliest records are from the Bible
Bible
The Bible refers to any one of the collections of the primary religious texts of Judaism and Christianity. There is no common version of the Bible, as the individual books , their contents and their order vary among denominations...

, as well as early Hindu
Hindu
Hindu refers to an identity associated with the philosophical, religious and cultural systems that are indigenous to the Indian subcontinent. As used in the Constitution of India, the word "Hindu" is also attributed to all persons professing any Indian religion...

 records. Early cataract surgery was developed by the Indian surgeon
Ayurveda
Ayurveda or ayurvedic medicine is a system of traditional medicine native to India and a form of alternative medicine. In Sanskrit, words , meaning "longevity", and , meaning "knowledge" or "science". The earliest literature on Indian medical practice appeared during the Vedic period in India,...

, Sushruta (6th century BCE). The Indian tradition of cataract surgery was performed with a special tool called the jabamukhi salaka, a curved needle used to loosen the lens and push the cataract out of the field of vision. The eye would later be soaked with warm butter and then bandaged. Though this method was successful, Sushruta cautioned that it should only be used when necessary. Greek physicians and philosophers
Greek philosophy
Ancient Greek philosophy arose in the 6th century BCE and continued through the Hellenistic period, at which point Ancient Greece was incorporated in the Roman Empire...

 traveled to India where these surgeries were performed by physicians. The removal of cataract by surgery was also introduced into China
Traditional Chinese medicine
Traditional Chinese Medicine refers to a broad range of medicine practices sharing common theoretical concepts which have been developed in China and are based on a tradition of more than 2,000 years, including various forms of herbal medicine, acupuncture, massage , exercise , and dietary therapy...

 from India.

The first references to cataract and its treatment in Ancient Rome
Ancient Rome
Ancient Rome was a thriving civilization that grew on the Italian Peninsula as early as the 8th century BC. Located along the Mediterranean Sea and centered on the city of Rome, it expanded to one of the largest empires in the ancient world....

 are found in 29 CE in De Medicinae, the work of the Latin encyclopedist Aulus Cornelius Celsus
Aulus Cornelius Celsus
Aulus Cornelius Celsus was a Roman encyclopedist, 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 diet, pharmacy, surgery and related fields, and it is one of the best sources...

. The Romans were pioneers in the health arena—particularly in the area of eye care.

The Muslim ophthalmologist
Ophthalmology in medieval Islam
Ophthalmology was one of the foremost branches in medieval Islamic medicine. The oculist or kahhal , a somewhat despised professional in Galen’s time, was an honored member of the medical profession by the Abbasid period, occupying a unique place in royal households...

 Ammar ibn Ali, in his Choice of Eye Diseases, written circa 1000 CE, wrote of his invention of the hypodermic needle and how he discovered the technique of cataract extraction while experiment
Experiment
An experiment is a methodical procedure carried out with the goal of verifying, falsifying, or establishing the validity of a hypothesis. Experiments vary greatly in their goal and scale, but always rely on repeatable procedure and logical analysis of the results...

ing with it on a patient.

Classification

The following is a classification of the various types of cataracts. This is not comprehensive, and other unusual types may be noted.
  • Classified by etiology
  • Age-related cataract
  • Cortical senile cataract
  • Immature senile cataract (IMSC): partially opaque lens, disc
    Optic disc
    The optic disc or optic nerve head is the location where ganglion cell axons exit the eye to form the optic nerve. There are no light sensitive rods or cones to respond to a light stimulus at this point. This causes a break in the visual field called "the blind spot" or the "physiological blind spot"...

     view hazy
  • Mature senile cataract (MSC): completely opaque lens, no disc view
  • Hypermature senile cataract (HMSC): liquefied cortical matter: Morgagnian cataract
  • Senile nuclear cataract
  • Cataracta brunescens
  • Cataracta nigra
  • Cataracta rubra
    • Congenital cataract
  • Sutural cataract
  • Lamellar cataract
  • Zonular cataract
    Zonular cataract and nystagmus
    Zonular cataract and nystagmus, also referred as Nystagmus with congenital zonular cataract is a rare congenital disease associated with Nystagmus and zonular cataract of the eye.-Genetics:...

  • Total cataract
    • Secondary cataract

  • Drug-induced cataract (e.g. corticosteroids)
    • Traumatic cataract
  • Blunt trauma (capsule usually intact)
  • Penetrating trauma (capsular rupture and leakage of lens material—calls for an emergency surgery for extraction of lens and leaked material to minimize further damage)

  • Classified by opacities, cataract can be classified by using Lens Opacities Classification System III (LOCS III: Nuclear NC1-5, Cortical C1-5 and Posterior P1-5. By application planning in procedures of phacoemulsification, LCOS III can be converted in newer cataract grading systems. Gede Pardianto (2009) introduced Optical Biometry Based Cataract Grading System (OBBCGS) that is helpful in cataract grading due to phacoemulsification planning. LOCS III's NC0, C0 and P0 can be converted as OBBCGS' no cataract (NC), LOCS III's NC1-3, C1-3, P1-4 can be converted to OBBCGS' Optical Biometry Examined Cataract (OBEC) and LOCS III's NC4-5, C4-5, P4-5 can be converted to OBBCGS's Optical Biometry Unexamined Cataract (OBUC); that need examination by Applanation Ultrasound Biometry.

  • Classified by location of opacity within lens structure (however, mixed morphology is quite commonly seen, e.g. PSC with nuclear changes and cortical spokes of cataract)
  • Anterior cortical cataract
  • Anterior polar cataract
  • Anterior subcapsular cataract

  • Nuclear cataract—grading correlates with hardness and difficulty of surgical removal
  • 1: Grey
  • 2: Yellow
  • 3: Amber
  • 4: Brown/black (Note: "black cataract" translated in some languages (like Hindi
    Hindi
    Standard Hindi, or more precisely Modern Standard Hindi, also known as Manak Hindi , High Hindi, Nagari Hindi, and Literary Hindi, is a standardized and sanskritized register of the Hindustani language derived from the Khariboli dialect of Delhi...

    ) refers to glaucoma
    Glaucoma
    Glaucoma is an eye disorder in which the optic nerve suffers damage, permanently damaging vision in the affected eye and progressing to complete blindness if untreated. It is often, but not always, associated with increased pressure of the fluid in the eye...

    , not the color of the lens nucleus)
    • Posterior cortical cataract
    • Posterior polar cataract (importance lies in higher risk of complication—posterior capsular tears during surgery)
    • Posterior subcapsular cataract (PSC) (clinically common)
    • After-cataract: posterior capsular opacification (PCO) subsequent to a successful extracapsular cataract surgery (usually within three months to two years) with or without IOL implantation. Requires a quick and painless office procedure with Nd:YAG laser
      Nd:YAG laser
      Nd:YAG is a crystal that is used as a lasing medium for solid-state lasers. The dopant, triply ionized neodymium, typically replaces yttrium in the crystal structure of the yttrium aluminium garnet , since they are of similar size...

       capsulotomy to restore optical clarity.

Signs and symptoms

As a cataract becomes more opaque, clear vision is compromised. A loss of visual acuity
Visual acuity
Visual acuity is acuteness or clearness of vision, which is dependent on the sharpness of the retinal focus within the eye and the sensitivity of the interpretative faculty of the brain....

 is noted. Contrast sensitivity
Contrast (vision)
Contrast is the difference in visual properties that makes an object distinguishable from other objects and the background. In visual perception of the real world, contrast is determined by the difference in the color and brightness of the object and other objects within the same field of view...

 is also lost, so that contours, shadows and color vision are less vivid. Veiling glare can be a problem as light is scattered by the cataract into the eye. The affected eye will have an absent red reflex. A contrast sensitivity test should be performed, and if a loss in contrast sensitivity is demonstrated, an eye specialist consultation is recommended.

It may be advisable to seek medical opinion, particularly in high-risk groups such as diabetics, if a "halo" is observed around street lights at night, especially if this phenomenon appears to be confined to one eye only.

The symptoms of cataracts are very similar to the symptoms of ocular citrosis
Ocular citrosis
Ocular Citrosis is a common infection of the eye generally resulting from periodic exposure to acidic substances, such as citrus fruit. It was first documented by Scottish physician Douglas Maclagan in 1860.-Causes:...

.

Causes

Cataracts develop for a variety of reasons, including long-term exposure to ultraviolet light, exposure to radiation, secondary effects of diseases such as diabetes, hypertension
Hypertension
Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...

 and advanced age, or trauma (possibly much earlier); they are usually a result of denaturation
Denaturation (biochemistry)
Denaturation is a process in which proteins or nucleic acids lose their tertiary structure and secondary structure by application of some external stress or compound, such as a strong acid or base, a concentrated inorganic salt, an organic solvent , or heat...

 of lens protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

. Genetic
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....

 factors are often a cause of congenital cataracts, and positive family history may also play a role in predisposing someone to cataracts at an earlier age, a phenomenon of "anticipation" in presenile cataracts. Cataracts may also be produced by eye injury
Eye injury
Physical or chemical injuries of the eye can be a serious threat to vision if not treated appropriately and in a timely fashion. The most obvious presentation of ocular injuries is redness and pain of the affected eyes. This is not, however, universally true, as tiny metallic projectiles may cause...

 or physical trauma
Physical trauma
Trauma refers to "a body wound or shock produced by sudden physical injury, as from violence or accident." It can also be described as "a physical wound or injury, such as a fracture or blow." Major trauma can result in secondary complications such as circulatory shock, respiratory failure and death...

. A study among Icelandair
Icelandair
Icelandair ehf is the flag carrier airline of Iceland, based on the grounds of Reykjavík Airport in Reykjavík. It is part of the Icelandair Group and currently operates scheduled services to 31 cities in 13 countries on both sides of the Atlantic Ocean out of its hub at Keflavík International Airport...

 pilots showed commercial airline pilots are three times more likely to develop cataracts than people with nonflying jobs. This is thought to be caused by excessive exposure to radiation coming from outer space
Outer space
Outer space is the void that exists between celestial bodies, including the Earth. It is not completely empty, but consists of a hard vacuum containing a low density of particles: predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, and neutrinos....

. Supporting this theory is the report that 33 of the 36 Apollo astronauts involved in the nine Apollo missions to leave Earth orbit have developed early stage cataracts that have been shown to be caused by radiation exposure to cosmic rays during their trip. At least 39 former astronauts have developed cataracts; 36 of those were involved in high-radiation missions such as the Apollo missions. Cataracts are also unusually common in persons exposed to infrared radiation, such as glassblowers
Glassblowing
Glassblowing is a glassforming technique that involves inflating molten glass into a bubble, or parison, with the aid of a blowpipe, or blow tube...

, who suffer from "exfoliation syndrome". Exposure to microwave radiation can cause cataracts. Atopic or allergic conditions are also known to quicken the progression of cataracts, especially in children. Cataracts can also be caused by iodine deficiency
Iodine deficiency
Iodine is an essential trace element; the thyroid hormones thyroxine and triiodotyronine contain iodine. In areas where there is little iodine in the diet—typically remote inlandareas where no marine foods are eaten—iodine deficiency gives rise to...

.

Cataracts may be partial or complete, stationary or progressive, hard or soft.

Some drugs can induce cataract development, such as corticosteroid
Corticosteroid
Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex. Corticosteroids are involved in a wide range of physiologic systems such as stress response, immune response and regulation of inflammation, carbohydrate metabolism, protein catabolism, blood electrolyte...

s and Seroquel.

There are various types of cataracts, e.g. nuclear, cortical, mature, and hypermature. Cataracts are also classified by their location, e.g. posterior (classically due to steroid use) and anterior (common (senile) cataract related to aging).

Associations with systemic conditions

  • Chromosomal disorders
  • 1q21.1 deletion syndrome
    1q21.1 deletion syndrome
    1q21.1 deletion syndrome or 1q21.1 microdeletion is a rare aberration of chromosome 1. , the international rare chromosome disorder group, has 48 genetically confirmed registered cases of this deletion worldwide ....

  • Cri-du-chat syndrome
  • Patau's syndrome
  • Schmid-Fraccaro syndrome
  • Trisomy 18 (Edward's syndrome)
  • Turner's syndrome
  • Single-gene disorders
  • Alport's syndrome
  • Conradi's syndrome
  • Myotonic dystrophy
    Myotonic dystrophy
    Myotonic dystrophy is a chronic, slowly progressing, highly variable inherited multisystemic disease. It is characterized by wasting of the muscles , cataracts, heart conduction defects, endocrine changes, and myotonia. Myotonic dystrophy can occur in patients of any age...

  • Autosomal dominant severe keratoconus with anterior polar cataract caused by mutation of the miR-184 seed region
  • Disease of the skin
    Skin
    -Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...

     and mucous membrans
  • Atopic dermatitis
    Atopic dermatitis
    Atopic dermatitis is an inflammatory, chronically relapsing, non-contagious and pruritic skin disorder...

  • Basal-cell nevus syndrome
  • Ichthyosis
    Ichthyosis
    Ichthyosis is a heterogeneous family of at least 28, generalized, mostly genetic skin disorders. All types of ichthyosis have dry, thickened, scaly or flaky skin...

  • Pemphigus
    Pemphigus
    Pemphigus is a rare group of blistering autoimmune diseases that affect the skin and mucous membranes.In pemphigus, autoantibodies form against desmoglein. Desmoglein forms the "glue" that attaches adjacent epidermal cells via attachment points called desmosomes...

  • Metabolic and nutrition diseases
  • Aminoaciduria
    Aminoaciduria
    Aminoaciduria is the presence of amino acids in the urine. Small amounts of amino acids are also present in normal urine. Increased total urine amino acids may result from metabolic disorders, chronic liver disease or renal disorders. Aminoacidurias can be divided into primary and secondary...

     (Lowe's syndrome)
  • Diabetes mellitus
    Diabetes mellitus
    Diabetes mellitus, often simply referred to as diabetes, is a group of metabolic diseases in which a person has high blood sugar, either because the body does not produce enough insulin, or because cells do not respond to the insulin that is produced...

  • Fabry's disease
    Fabry's disease
    Fabry disease is a rare X-linked recessive lysosomal storage disease, which can cause a wide range of systemic symptoms...

  • Galactosemia
    Galactosemia
    Galactosemia is a rare genetic metabolic disorder that affects an individual's ability to metabolize the sugar galactose properly. Although the sugar lactose can metabolize to galactose, galactosemia is not related to and should not be confused with lactose intolerance...

     / galactosemic cataract
    Galactosemic Cataract
    A Galactosemic cataract is cataract which is associated with the consequences of galactosemia.-Galactosemia:Galactosemia is one of the most mysterious of the heavily-researched metabolic diseases. It is a hereditary disease that results in a defect in, or absence of, galactose-metabolizing enzymes...

  • Homocystinuria
    Homocystinuria
    Homocystinuria, also known as cystathionine beta synthase deficiency or CBS deficiency, is an inherited disorder of the metabolism of the amino acid methionine, often involving cystathionine beta synthase...

  • Hyperparathyroidism
    Hyperparathyroidism
    Hyperparathyroidism is overactivity of the parathyroid glands resulting in excess production of parathyroid hormone . The parathyroid hormone regulates calcium and phosphate levels and helps to maintain these levels...

  • Hypervitaminosis D
    Hypervitaminosis D
    Hypervitaminosis D is a state of vitamin D toxicity.The recommended daily allowance is 400 IU per day. Overdose has been observed at 1925 µg/d...

  • Hypothyroidism
    Hypothyroidism
    Hypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone.Iodine deficiency is the most common cause of hypothyroidism worldwide but it can be caused by other causes such as several conditions of the thyroid gland or, less commonly, the pituitary gland or...

  • Mucopolysaccharidoses
  • Wilson's disease
    Wilson's disease
    Wilson's disease or hepatolenticular degeneration is an autosomal recessive genetic disorder in which copper accumulates in tissues; this manifests as neurological or psychiatric symptoms and liver disease...

  • Infectious disease
    Infectious disease
    Infectious diseases, also known as communicable diseases, contagious diseases or transmissible diseases comprise clinically evident illness resulting from the infection, presence and growth of pathogenic biological agents in an individual host organism...

    s
  • Congenital
  • Congenital herpes simplex
  • Congenital syphilis
    Congenital syphilis
    Congenital syphilis is syphilis present in utero and at birth, and occurs when a child is born to a mother with secondary syphilis. Untreated syphilis results in a high risk of a bad outcome of pregnancy, including mulberry molars in the fetus. Syphilis can cause miscarriages, premature births,...

  • Cytomegalic inclusion disease
  • Rubella
    Rubella
    Rubella, commonly known as German measles, is a disease caused by the rubella virus. The name "rubella" is derived from the Latin, meaning little red. Rubella is also known as German measles because the disease was first described by German physicians in the mid-eighteenth century. This disease is...

    • Others
  • Cysticercosis
    Cysticercosis
    Cysticercosis refers to tissue infection after exposure to eggs of Taenia solium, the pork tapeworm. The disease is spread via the fecal-oral route through contaminated food and water, and is primarily a food borne disease. After ingestion the eggs pass through the lumen of the intestine into the...

  • Leprosy
    Leprosy
    Leprosy or Hansen's disease is a chronic disease caused by the bacteria Mycobacterium leprae and Mycobacterium lepromatosis. Named after physician Gerhard Armauer Hansen, leprosy is primarily a granulomatous disease of the peripheral nerves and mucosa of the upper respiratory tract; skin lesions...

  • Onchocerciasis
    Onchocerciasis
    Onchocerciasis , also known as river blindness and Robles' disease, is a parasitic disease caused by infection by Onchocerca volvulus, a nematode . Onchocerciasis is the world's second-leading infectious cause of blindness. It is not the nematode, but its endosymbiont, Wolbachia pipientis, that...

  • Toxoplasmosis
    Toxoplasmosis
    Toxoplasmosis is a parasitic disease caused by the protozoan Toxoplasma gondii. The parasite infects most genera of warm-blooded animals, including humans, but the primary host is the felid family. Animals are infected by eating infected meat, by ingestion of feces of a cat that has itself...

    • Toxic substances introduced systemically
    • Corticosteroids
    • Haloperidol
      Haloperidol
      Haloperidol is a typical antipsychotic. It is in the butyrophenone class of antipsychotic medications and has pharmacological effects similar to the phenothiazines....

    • Miotics
    • Triparanol

Prevention

Although cataracts have no scientifically proven prevention, wearing ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

-protecting sunglasses
Sunglasses
Sunglasses or sun glasses 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 sometimes also function as a visual aid, as variously termed spectacles or glasses exist, featuring lenses that...

 may slow the development of cataracts. Regular intake of antioxidants (such as vitamins A, C and E) is theoretically helpful, but taking them as a supplement has not been shown to have a benefit. The less well-known antioxidant N-acetylcarnosine has been shown in randomized controlled clinical trials to treat cataracts, and can be expected to prevent their formation by similar mechanisms. N-acetylcarnosine is a proposed treatment for other ocular disorders that are instigated, or exacerbated, by oxidative stress, including glaucoma, retinal degeneration, corneal disorders, and ocular inflammation.

Surgical

The operation to remove cataracts can be performed at any stage of their development. There is no longer a reason to wait until a cataract is "ripe" before removing it. However, because all surgery involves some risk, it is usually worth waiting until there is some change in vision before removing the cataract.

The most effective and common treatment is to make an incision (capsulotomy) into the capsule of the cloudy lens to surgically remove it. Two types of eye surgery
Eye surgery
Eye surgery, also known as orogolomistician surgery or ocular surgery, is surgery performed on the eye or its adnexa, typically by an ophthalmologist.-Preparation and precautions:...

 can be used to remove cataracts: extracapsular cataract extraction (ECCE) and intracapsular cataract extraction (ICCE).

ECCE surgery consists of removing the lens, but leaving the majority of the lens capsule
Lens capsule
The lens capsule is a component of the eye. It is a clear, membrane-like structure that is quite elastic, a quality that keeps it under constant tension. As a result, the lens naturally tends towards a rounder or more globular configuration, a shape it must assume for the eye to focus at a near...

 intact. High frequency
High frequency
High frequency radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters . Frequencies immediately below HF are denoted Medium-frequency , and the next higher frequencies are known as Very high frequency...

 sound waves (phacoemulsification
Phacoemulsification
Phacoemulsification refers to modern cataract surgery in which the eye's internal lens is emulsified with an ultrasonic handpiece and aspirated from the eye...

) are sometimes used to break up the lens before extraction.

Intra-capsular (ICCE) surgery involves removing the entire lens of the eye, including the lens capsule, but it is rarely performed in modern practice.

In either extracapsular surgery or intracapsular surgery, the cataractous lens is removed and replaced with a plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...

 lens (an intraocular lens
Intraocular lens
An intraocular lens is an implanted lens in the eye, usually replacing the existing crystalline lens because it has been clouded over by a cataract, or as a form of refractive surgery to change the eye's optical power. It usually consists of a small plastic lens with plastic side struts, called...

 implant) which stays in the eye permanently.

Cataract operations are usually performed using a local anaesthetic, and the patient is allowed to go home the same day. Recent improvements in intraocular technology now allow cataract patients to choose a multifocal lens to create a visual environment in which they are less dependent on glasses. Such multifocal lenses are flexible and can be controlled using the same eye muscles used to control the natural lens. Under some medical systems, multifocal lenses cost extra. Traditional intraocular lenses are monofocal.

Complications are possible after cataract surgery, including endophthalmitis
Endophthalmitis
Endophthalmitis is an inflammation of the internal coats of the eye. It is a dreaded complication of all intraocular surgeries, particularly cataract surgery, with possible loss of vision and the eye itself. Infectious etiology is the most common and various bacteria and fungi have been isolated as...

, posterior capsular opacification and retinal detachment
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 blindness. It is a medical emergency.The retina is a...

.

Research

Research is scant and mixed, but weakly positive, for the nutrients lutein and zeaxanthin. Bilberry
Bilberry
Bilberry is any of several species of low-growing shrubs in the genus Vaccinium , bearing edible berries. The species most often referred to is Vaccinium myrtillus L., but there are several other closely related species....

 extract shows promise in rat models and in clinical studies.

Investigational treatments

In the past few years, eye drops containing acetyl-carnosine
Acetyl-carnosine
N-Acetylcarnosine is a naturally occurring compound chemically related to the dipeptide carnosine. Its molecular structure is similar to carnosine with the exception that it carries an additional acetyl group...

 have been used by several thousands of cataract patients across the world. The drops are believed to work by reducing oxidation and glycation
Glycation
Glycation is the result of the bonding of a protein or lipid molecule with a sugar molecule, such as fructose or glucose, without the controlling action of an enzyme. All blood sugars are reducing molecules. Glycation may occur either inside the body or outside the body...

 damage in the lens, particularly reducing crystallin
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 cancer tumors....

 crosslinking. Randomized controlled trials indicate the drops may be especially appropriate for seniors, or others where surgery is not advised.

Investigational preventives

Although statins are known for their ability to lower lipids, they are also believed to have antioxidant qualities. Oxidative stress is believed to play a role in the development of nuclear cataracts, which are the most common type of age-related cataracts. To explore the relationship between nuclear cataracts and statin use, a group of researchers treated a group of 1299 patients who were at risk of developing nuclear cataracts with statins. Their results suggest statin use in an at-risk population may be associated with a lower risk of developing nuclear cataract disease.

Long term (average five year) observation showed systematic application of azapentacene sodium polysulfonate (Quinax) slows down the progress of the disease.

See also


External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
x
OK