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Cataract

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Cataract
SpecialtyOphthalmology Edit this on Wikidata
Human eye cross-sectional view, showing position of human lens. Courtesy NIH National Eye Institute
File:Ferrets (Sandy & Star) (3).JPG
Image showing cataracts in the eyes of a ferret.
For other uses, see Cataract (disambiguation).

A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity 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), 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]

A senile cataract, occurring in the aged, is characterized by an initial opacity in the lens, subsequent swelling of the lens and final shrinkage with complete loss of transparency.[2] 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. 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) in ancient times were regarded as a blessing from the heavens, because some perception of light was restored in the cataractous 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"[3]). 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",[4] so it is also possible that the name came about through the sense 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.[5] In dialect English a cataract is called a pearl, as in "pearl eye" and "pearl-eyed".[6]

Causes

Cataracts develop from a variety of reasons, including long-term exposure to ultraviolet light, exposure to radiation, secondary effects of diseases such as diabetes, hypertension and advanced age, or trauma (possibly much earlier); they are usually a result of denaturation of lens protein. 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 may 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.[7] 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, such as Corticosteroids[8] and Ezetimibe[citation needed] 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[8][9]) and anterior (common (senile) cataract related to aging).

Epidemiology

Age-related cataract is responsible for 48% of world blindness, which represents about 18 million people, according to the World Health Organization (WHO).[10] 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 to 64,[11] 60% of those between the ages 65 and 74,[12] and 91% of those between the ages of 75 and 85.[11]

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 earliest records are from the Bible as well as early Hindu records.[13] Early cataract surgery was developed by the Indian surgeon, Sushruta (6th century BCE).[14] The Indian traditions 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.[14] The eye would later be soaked with warm butter and then bandaged.[14] Though this method was successful, Susruta cautioned that it should only be used when necessary.[14] Greek physicians and philosophers traveled to India where these surgeries were performed by physicians.[14] The removal of cataract by surgery was also introduced into China from India.[15]

The first references to cataract and its treatment in Ancient Rome are found in 29 AD in De Medicinae, the work of the Latin encyclopedist Aulus Cornelius Celsus.[16] The Romans were pioneers in the health arena - particularly in the area of eye care.[17]

The Iraqi ophthalmologist Ammar ibn Ali of Mosul performed the first extraction of cataracts through suction. He invented a hollow metallic syringe hypodermic needle, which he applied through the sclerotic and extracted the cataracts using suction.[18] In his Choice of Eye Diseases, written in circa 1000, he wrote of his invention of the hypodermic needle and how he discovered the technique of cataract extraction while experimenting with it on a patient.[19]

When a cataract is sufficiently developed to be removed by surgery, the most effective and common treatment is to make an incision (capsulotomy) into the capsule of the cloudy lens in order to surgically remove the lens. There are two types of eye surgery that can be used to remove cataracts: extra-capsular (extracapsular cataract extraction, or ECCE) and intra-capsular (intracapsular cataract extraction, or ICCE).

Extra-capsular (ECCE) 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 (ICCE) 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 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. Under some medical systems multifocal lenses cost extra. Traditional intraocular lenses are monofocal.

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

In ICCE there is the issue of the Jack in the box phenomenon[clarification needed] where the patient has to wear aphakic glasses - alternatives include contact lenses but these can prove to be high maintenance, particularly in dusty areas.

Prevention

Although cataracts have no scientifically proven prevention, it is sometimes said that wearing ultraviolet-protecting sunglasses may slow the development of cataracts.[20][21] Regular intake of antioxidants (such as vitamin A, C and E) is theoretically helpful, but taking them as a supplement has been shown to have no benefit.[22]

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 an at-risk population may be associated with a lower risk of developing nuclear cataract disease.[23]

Research is scant and mixed but weakly positive for the nutrients lutein and zeaxanthin.[24][25][26][27] Bilberry extract shows promise in rat models [28][29] and in clinical studies.[30]

In the past few years, eye drops containing acetyl-carnosine have been used by several thousands cataract patients across the world. The drops are believed to work by reducing oxidation and glycation damage in the lens, particularly reducing cristallin cross-linking [31], [32]. The use of these drops remains controversial due to lack of large properly designed trials.

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
  • Secondary cataract
Slit lamp photo of Anterior capsular opacification visible a 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 minimize 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 a 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 capsular 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.

Associations with systemic conditions

  • Congenital
  • Others
  • Toxic substances introduced systemically

See also

References and notes

  • Pavan-Langston, Deborah (1990). Manual of Ocular Diagnosis and Therapy. Little, Brown and Company.
  1. ^ Common Causes of Vision Loss in Elderly Patients - July 1999 - American Academy of Family Physicians
  2. ^ eMedicine - Cataract, Senile : Article by Vicente Victor D Ocampo. From eMedicine The Continually Updated Clinical Reference
  3. ^ Dictionary.com/Word of the Day Archive/cataract
  4. ^ Online Etymology Dictionary
  5. ^ Mistaken Science - Topic Powered by eve community. Wordcraft Forums
  6. ^ Webster's Revised Unabridged Dictionary (1913 edition). Public Reference Tools - The ARTFL Project (American and French Research on the Treasury of the French Laanguage), University of Chicago
  7. ^ Rafnsson, V (2005). "Cosmic radiation increases the risk of nuclear cataract in airline pilots: a population-based case-control study". Arch Ophthalmol. 123: 1102–1105. doi:10.1001/archopht.123.8.1102. PMID 16087845. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  8. ^ a b SPENCER R, ANDELMAN S. "Steroidsarebad Cataracts. Posterior Subcapsular Cataract Formation In Rheumatoid Arthritis Patients On Long Term Steroid Therapy". Arch Ophthalmol. 74: 38–41. PMID 14303339.
  9. ^ Greiner J, Chylack L (1979). "Posterior subcapsular cataracts: histopathologic study of steroid-associated cataracts". Arch Ophthalmol. 97 (1): 135–44. PMID 758890.
  10. ^ WHO | Priority eye diseases.
  11. ^ 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.
  12. ^ 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.
  13. ^ A short history of cataract surgery
  14. ^ a b c d e Finger, page 66
  15. ^ Lade & Svoboda, page 85
  16. ^ Cataract history
  17. ^ The Romans carried out cataract ops, February 9, 2008, BBC News
  18. ^ Ibrahim B. Syed PhD, "Islamic Medicine: 1000 years ahead of its times", Journal of the International Society for the History of Islamic Medicine 2 (2002): 2-9 [7].
  19. ^ Finger, Stanley (1994), Origins of Neuroscience: A History of Explorations Into Brain Function, Oxford University Press, p. 70, ISBN 0195146948
  20. ^ Epidemiology. 2003 Nov;14(6):707-12. Sun exposure as a risk factor for nuclear cataract
  21. ^ J.C. Javitt, F. Wang and S. K. West, “Blindness Due to Cataract: Epidemiology and Prevention.” Annual Review of Public Health 17 (1996): 159-77. Cited in Five-Year Agenda for the National Eye Health Education Program (NEHEP), p. B-2; National Eye Institute, U.S. National Institutes of Health
  22. ^ A randomized, placebo-controlled, clinical trial of high-dose supplementation with vitamins C and E and beta carotene for age-related cataract and vision loss: AREDS report no. 9. Arch Ophthalmol. 2001 Oct;119(10):1439-52
  23. ^ Klein, Barbara (2006). "Statin Use and Incident Nuclear Cataract". Journal of the American Medical Association. 295 (23): 2752–2758. doi:10.1001/jama.295.23.2752. PMID 16788130. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  24. ^ Nutrition. 2003 Jan;19(1):21 Lutein, but not alpha-tocopherol, supplementation improves visual function] in patients with age-related cataracts: a 2-y double-blind, placebo-controlled pilot study
  25. ^ Invest Ophthalmol Vis Sci. 2006 Sep;47(9):3783-6. Lutein and zeaxanthin and the risk of cataract: the Melbourne visual impairment project
  26. ^ Invest Ophthalmol Vis Sci. 2006 Jun;47(6):2329-35. Plasma lutein and zeaxanthin and other carotenoids as modifiable risk factors for age-related maculopathy and cataract: the POLA Study
  27. ^ J Am Coll Nutr. 2004 Dec;23(6 Suppl):567S-587S Lutein and zeaxanthin and their potential roles in disease prevention
  28. ^ Dietary supplementation with bilberry extract prevents macular degeneration and cataracts in senesce-accelerated OXYS rats Adv Gerontol. 2005;16:76-9
  29. ^ Yamakoshi J, et al. J Agric Food Chem. 2002 Aug 14;50(17):4983-8.
  30. ^ Ann Ottalmol Clin Ocul, 1989
  31. ^ Williams DL, Munday P. The effect of a topical antioxidant formulation including N-acetyl carnosine on canine cataract: a preliminary study. Vet Ophthalmol. 2006;9(5):311-6
  32. ^ Guo Y, Yan H. Preventive effect of carnosine on cataract development. Yan Ke Xue Bao. 2006; 22(2):85-8
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