Cataract

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For other uses, see Cataract (disambiguation).

**Cataract**
*Classification & external resources*

Magnified view of cataract in human eye, seen on examination with a slit lamp using diffuse illumination
ICD-10	H 25.-H 26., H 28., Q 12.0
ICD-9	366
DiseasesDB	2179
MedlinePlus	001001

Human eye cross-sectional view, showing position of human lens. Courtesy NIH National Eye Institute

A cataract is an opacity that develops in the crystalline lens of the eye or in its envelope. Early on in the development of senile cataract the power of the crystaline lens may be increased, causing myopia, and the gradual yellowing and opacification of the lens may reduce the perception of blue colours. Cataracts typically progress slowly to cause vision loss and are potentially blinding if untreated.^[1] Moreover, with time the cataract cortex liquefies to form a milky white fluid in a Morgagnian Cataract, and can cause severe inflammation if the lens capsule ruptures and leaks. Untreated, the cataract can cause phacomorphic glaucoma. Very advanced cataracts with weak zonules are liable to dislocation anteriorly or posteriorly. Such spontaneous posterior dislocations (akin to the earliest surgical procedure of couching) in ancient times were regarded as a blessing from the heavens, because it restored some perception of light in the bilaterally affected patients.

Cataract derives from the Latin cataracta meaning "waterfall" and the Greek kataraktes and katarrhaktes, from katarassein meaning "to dash down" (kata-, "down"; arassein, "to strike, dash"^[2]). 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"^[3], so it is also possible that the name came about through the sense of "obstruction".

1 Causes
2 Epidemiology
3 Cataract surgery
4 Prevention
5 Recent research
6 Types of cataracts
7 Associations with systemic conditions
8 References
9 See also
10 External links

[edit] Causes

Normal vision. Courtesy National Institutes of Health, USA (NIH).

Hazy view as seen by a person with a cataract, Courtesy NIH

Cataracts develop from a variety of reasons, including long-term ultraviolet exposure, secondary effects of diseases such as diabetes, or simply due to advanced age; they are usually a result of denaturation of lens proteins. Genetic 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 pre-senile cataracts. Cataracts can also be produced by eye injury or physical trauma. A study among Icelandair pilots showed commercial airline pilots as three times more likely to develop cataracts than people with non-flying jobs. This is thought to be caused by excessive exposure to radiation coming from outer space.^[4] Cataracts are also unusually common in persons exposed to infrared radiation, such as glassblowers who suffer from "exfoliation syndrome". Exposure to microwave radiation can cause cataracts.

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

Some drugs can induce cataract development:

There are various types of cataracts, e.g. nuclear, cortical, mature, hypermature. Cataracts are also classified by their location, e.g. posterior (classically due to steroid use^[5]^[6]) and anterior (common (senile) cataract related to aging).

[edit] Epidemiology

Cataracts are the leading cause of blindness in the world.^[7]

In the United States, age-related lenticular changes have been reported in 42% of those between the ages of 52 to 64^[8], 60% of those between the ages 65 and 74^[9], and 91% of those between the ages of 75 and 85^[8].

[edit] Cataract surgery

Main article: Cataract surgery

Cataract surgery, using a temporal approach phacoemulsification probe (in right hand) and "chopper"(in left hand) being done under operating microscope at a Navy medical center

The most effective and common treatment is to surgically remove the cloudy lens. There are two types of surgery that can be used to remove cataracts, extra-capsular (extracapsular cataract extraction, or ECCE) and intra-capsular surgery (intracapsular cataract extraction, or ICCE). Extra-capsular surgery consists of removing the lens but leaving the majority of the lens capsule intact. High frequency sound waves (phacoemulsification) are sometimes used to break up the lens before extraction. Intra-capsular surgery involves removing the entire lens of the eye, including the lens capsule, but it is rarely performed in modern practice. In either extra-capsular surgery or intra-capsular surgery, the cataractous lens is removed and replaced with a plastic lens (an intraocular lens implant) which stays in the eye permanently.

Cataract operations are usually performed using a local anaesthetic and the patient will be 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 where they are less dependent on glasses. Traditional intraocular lenses were monofocal. Medicare has allowed physicians, for the first time, to bill patients for this advanced lens design.

Complications after cataract surgery, including posterior capsular opacification and retinal detachment, are possible.

In ICCE there is the issue of the Jack in the box Phenomenon where the patient has to wear aphakic glasses...alternatives include contact lenses but these can prove to be high maintainance in dusty areas, which can lead to the complications of contact lenses.

[edit] Prevention

Although cataracts have no scientifically proven prevention, it is sometimes said that wearing ultraviolet-protecting sunglasses may slow the development of cataracts.^{[citation needed]} Regular intake of antioxidants (such as vitamin C and E) is theoretically helpful, but this is also not proven.

[edit] Recent research

Although statins are known for their ability to lower lipids, they are also believed to have antioxidant qualities. It is believed that oxidative stress plays a role in the development of nuclear cataracts, which are the most common type of age-related cataract. To explore the relationship between nuclear cataracts and statin use, a group of researchers took a group of 1299 patients who were at risk of developing nuclear cataracts and gave some of them statins. Their results suggest that statin use in a general population may be associated with a lower risk of developing nuclear cataract. ^[10]

[edit] Types of cataracts

Bilateral cataracts in an infant due to Congenital rubella syndrome, courtesy CDC

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

Immature Senile Cataract (IMSC) - partially opaque lens, disc view hazy
Mature Senile Cataract (MSC) - Completely opaque lens, no disc view
Hypermature Senile Cataract (HMSC) - Liquefied cortical matter: Morgagnian Cataract

Congenital cataract

Sutural cataract
Lamellar cataract
Zonular cataract
Total cataract

Secondary cataract

Slit lamp photo of Anterior capsular opacification visible few months after implantation of Intraocular lens in eye, magnified view

Drug-induced cataract (e.g. Corticosteroids)

Traumatic cataract

Blunt trauma (capsule usually intact)
Penetrating trauma (capsular rupture & leakage of lens material - calls for an emergency surgery for extraction of lens and leaked material to minimise further damage)

Classified by location of opacity within lens structure (However, mixed morphology is quite commonly seen, e.g. PSC with nuclear changes & cortical spokes of cataract)

Anterior cortical cataract
Anterior polar cataract
Anterior subcapsular cataract

Slit lamp photo of Posterior capsular opacification visible few months after implantation of Intraocular lens in eye, seen on retroillumination

Nuclear cataract - Grading correlates with hardness & difficulty of surgical removal

1 - Grey
2 - Yellow
3 - Amber
4 - Brown/Black (Note: "Black cataract" translated in some languages (like Hindi) refers to Glaucoma, not the color of the lens nucleus)

Posterior cortical cataract
Posterior polar cataract (importance lies in higher risk of complication - posterior capuslar tears during surgery)
Posterior subcapsular cataract (PSC) (clinically common)

After-cataract - posterior capsular opacification subsequent to a successful extracapsular cataract surgery (usually within 3 months - 2 years) with or without IOL implantation. Requires a quick & painless office procedure with Nd:YAG laser capsulotomy to restore optical clarity.

[edit] Associations with systemic conditions

Chromosomal disorders

Alport's syndrome
Cri-du-chat syndrome
Conradi's syndrome
Myotonia dystrophica
Patau's syndrome
Schmid-Fraccaro syndrome
Trisomy 18 (Edward's syndrome)
Turner's syndrome

Disease of the skin and mucous membranes

Atopic dermatitis
Basal-cell nevus syndrome
Ichthyosis
Pemphigus

Metabolic and nutrition diseases

Infectious diseases

Congenital

Others

Toxic substances introduced systemically

[edit] References

^ http://www.aafp.org/afp/990700ap/99.html
^ http://dictionary.reference.com/wordoftheday/archive/2003/10/29.html]
^ http://www.etymonline.com/index.php?term=cataract
^ Rafnsson, V; Olafsdottir E, Hrafnkelsson J, Sasaki H, Arnarsson A, Jonasson F. "Cosmic radiation increases the risk of nuclear cataract in airline pilots: a population-based case-control study". Arch Ophthalmol 123: 1102-1105.
^ ^a ^b SPENCER R, ANDELMAN S. "STEROID CATARACTS. POSTERIOR SUBCAPSULAR CATARACT FORMATION IN RHEUMATOID ARTHRITIS PATIENTS ON LONG TERM STEROID THERAPY". Arch Ophthalmol 74: 38-41. PMID 14303339.
^ Greiner J, Chylack L (1979). "Posterior subcapsular cataracts: histopathologic study of steroid-associated cataracts". Arch Ophthalmol 97 (1): 135-44. PMID 758890.
^ https://web.emmes.com/study/areds/mopfiles/chp2_mop.pdf
^ ^a ^b Sperduto RD, Seigel D. Sperduto RD, Seigel D. "Senile lens and senile macular changes in a population-based sample." Am J Ophthalmol. 1980 Jul;90(1):86-91. PMID 7395962.
^ Kahn HA, Leibowitz HM, Ganley JP, Kini MM, Colton T, Nickerson RS, Dawber TR. "The Framingham Eye Study. I. Outline and major prevalence findings." Am J Epidemiol. 1977 Jul;106(1):17-32. PMID 879158.
^ Klein, Barbara; Ronald Klein, Kristine Lee, and Lisa Grady. "Statin Use and Incident Nuclear Cataract". Journal of the American Medical Association 295 (23): 2752-2758.