Editing Cataract (section)

== Causes ==

===Age===
Age is the most common cause of cataracts.<ref name=NIH2009/><ref name=WHOPri/> Lens proteins [[Denaturation (biochemistry)|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.<ref name="yanoff">{{cite book |title=Ophthalmology |vauthors=Duker JS, Yanoff M |publisher=Mosby/Elsevier |year=2009 |isbn=978-0-323-04332-8 |location=St. Louis, Missouri |language=en-us}}{{page needed|date=May 2016}}</ref>

[[Oxidative stress]] associated with [[lipid peroxidation]] is an important pathogenic mechanism in cataract formation.<ref name="Hsueh2022">{{cite journal | doi=10.3390/ijms23031255 | doi-access=free | title=The Pathomechanism, Antioxidant Biomarkers, and Treatment of Oxidative Stress-Related Eye Diseases | date=2022 | last1=Hsueh | first1=Yi-Jen | last2=Chen | first2=Yen-Ning | last3=Tsao | first3=Yu-Ting | last4=Cheng | first4=Chao-Min | last5=Wu | first5=Wei-Chi | last6=Chen | first6=Hung-Chi | journal=International Journal of Molecular Sciences | volume=23 | issue=3 | page=1255 | pmid=35163178 | pmc=8835903 }}</ref><ref>{{Cite journal|title=Lipid peroxidation: pathophysiological and pharmacological implications in the eye|first1=Ya Fatou|last1=Njie-Mbye|first2=Madhura|last2=Chitnis|first3=Catherine|last3=Opere|first4=Sunny|last4=Ohia|date=January 18, 2013|journal=Frontiers in Physiology|volume=4|page=366 |doi=10.3389/fphys.2013.00366|doi-access=free |pmid=24379787 |pmc=3863722}}</ref> Senile cataracts are associated with a decrease in [[antioxidant]] capacity in the lens.<ref name = Hsueh2022/> 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.<ref name = Hsueh2022/>

===Trauma===
[[File:Rosette cataract.jpg|thumb|Post traumatic rosette cataract of a 60-year-old male]]
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 injury|electrical injuries]].<ref>{{cite journal | vauthors = Reddy SC | title = Electric cataract: a case report and review of the literature | journal = European Journal of Ophthalmology | volume = 9 | issue = 2 | pages = 134–138 | year = 1999 | pmid = 10435427 | doi = 10.1177/112067219900900211 | s2cid = 45814684 }}</ref> Blunt trauma can also result in star- (stellate) or petal-shaped cataracts.<ref>{{cite journal | vauthors = Ram J, Gupta R | title = Images in Clinical Medicine. Petaloid Cataract | journal = The New England Journal of Medicine | volume = 374 | issue = 18 | pages = e22 | date = May 2016 | pmid = 27144871 | doi = 10.1056/NEJMicm1507349 }}</ref>

===Radiation===
Cataracts can arise as an effect of exposure to various types of radiation. X-rays, one form of [[Radiobiology|ionizing radiation]], may damage the DNA of lens cells.<ref name = "Lipman1988">{{cite journal | vauthors = Lipman RM, Tripathi BJ, Tripathi RC | title = Cataracts induced by microwave and ionizing radiation | journal = Survey of Ophthalmology | volume = 33 | issue = 3 | pages = 200–210 | year = 1988 | pmid = 3068822 | doi = 10.1016/0039-6257(88)90088-4 }}</ref> Ultraviolet light, specifically [[UVB]], has also been shown to cause cataracts, and some evidence indicates sunglasses worn at an early age can slow its development in later life.<ref>{{cite journal | vauthors = Sliney DH | title = UV radiation ocular exposure dosimetry | journal = Documenta Ophthalmologica. Advances in Ophthalmology | volume = 88 | issue = 3–4 | pages = 243–254 | year = 1994 | pmid = 7634993 | doi = 10.1007/bf01203678 | s2cid = 8242055 }}</ref> [[microwave#Effects on health|Microwave]]s, a type of [[nonionizing radiation]], may cause harm by denaturing protective enzymes (e.g., [[glutathione peroxidase]]), by oxidizing [[Cysteine|protein thiol]] groups (causing [[protein aggregation]]), or by damaging lens cells via thermoelastic expansion.<ref name = "Lipman1988" /> The protein coagulation caused by electric and heat injuries whitens the lens.<ref name="yanoff" /> This same process is what makes the clear albumen of an egg become white and opaque during cooking.{{citation needed|date=June 2022}}

===Genetics===
[[File:Chrismas tree cataract.jpg|thumb|Christmas tree cataract (diffuse illumination)]]
The genetic component is strong in the development of cataracts,<ref>{{citation |page=77 |chapter=Molecular Genetics of Cataract |title=Genetics in Ophthalmology |publisher=Karger Medical and Scientific Publishers |year=2003 |isbn=978-3-8055-7578-2 | vauthors = Hejtmancik JF, Smaoui N }}</ref> 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 [[Chromosomal disorder|chromosome abnormalities]] associated with cataracts include [[1q21.1 deletion syndrome]], [[cri-du-chat syndrome]], [[Down syndrome]], [[Patau's syndrome]], [[trisomy 18]] ([[Edward's syndrome]]), and [[Turner's syndrome]], and in the case of [[neurofibromatosis type 2]], [[juvenile cataract]] on one or both sides may be noted. Examples of [[single-gene disorder]] include [[Alport's syndrome]], [[Conradi's syndrome]], [[cerebrotendineous xanthomatosis]], [[myotonic dystrophy]], and [[oculocerebrorenal syndrome]] or [[Lowe syndrome]].<ref>{{Cite journal |last1=Li |first1=Jinyu |last2=Xia |first2=Chun-hong |last3=Wang |first3=Eddie |last4=Yao |first4=Ke |last5=Gong |first5=Xiaohua |date=2017 |title=Screening, genetics, risk factors, and treatment of neonatal cataracts |journal=Birth Defects Research |language=en |volume=109 |issue=10 |pages=734–743 |doi=10.1002/bdr2.1050 |issn=2472-1727 |pmc=9211061 |pmid=28544770}}</ref>

===Skin diseases===
The skin and the lens have the same embryological origin and so can be affected by similar diseases.<ref>{{citation |page=507 |title=Ophthalmology | vauthors = Yanoff M, Duker JS |publisher=Elsevier Health Sciences |year=2009 |isbn=978-0-323-04332-8}}</ref> Those with [[atopic dermatitis]] and [[eczema]] occasionally develop shield ulcer cataracts.{{Citation needed|date=November 2024}} [[Ichthyosis]] is an autosomal recessive disorder associated with cuneiform cataracts and nuclear sclerosis. [[Nevoid basal-cell carcinoma syndrome|Basal-cell nevus]] and [[pemphigus]] have similar associations.{{citation needed|date=September 2022}}

===Smoking and alcohol===

[[Tobacco smoking|Cigarette smoking]] has been shown to increase the risk of age-related cataract and nuclear cataract.<ref>{{cite journal|year=2012|author=Ye J, He J, Wang C, Wu H, Shi X, Zhang H, Xie J, Lee SY.|title=Smoking and risk of age-related cataract: a meta-analysis|journal=Invest Ophthalmol Vis Sci|volume=53|issue=7|pages=3885–3895|doi=10.1167/iovs.12-9820|pmid=22599585}}</ref><ref>{{cite journal|year=2019|author=Beltrán-Zambrano E, García-Lozada D, Ibáñez-Pinilla E.|title= Risk of cataract in smokers: A meta-analysis of observational studies|journal=Arch Soc Esp Oftalmol (Engl Ed)|volume=94|issue=2|pages=60–74|doi=10.1016/j.oftal.2018.10.020|pmid=30528895|s2cid=155984835 }}</ref> Evidence is conflicting over the effect of alcohol. Some surveys have shown a link, but others that followed people over longer terms have not.<ref>{{cite journal | vauthors = Wang S, Wang JJ, Wong TY | title = Alcohol and eye diseases | journal = Survey of Ophthalmology | volume = 53 | issue = 5 | pages = 512–525 | year = 2008 | pmid = 18929762 | doi = 10.1016/j.survophthal.2008.06.003 }}</ref>

===Inadequate vitamin C===
Low [[vitamin C]] intake and serum levels have been associated with greater cataract rates.<ref name = "WeiLiang2016">{{cite journal | vauthors = Wei L, Liang G, Cai C, Lv J | title = Association of vitamin C with the risk of age-related cataract: a meta-analysis | journal = Acta Ophthalmologica | volume = 94 | issue = 3 | pages = e170–e176 | date = May 2016 | pmid = 25735187 | doi = 10.1111/aos.12688 | s2cid = 42785248 | doi-access = free }}</ref> However, use of supplements of vitamin C has not demonstrated benefit.<ref name=Matthew2012/>

===Medications===
Some medications, such as systemic, topical, or inhaled [[corticosteroid]]s, may increase the risk of cataract development.<ref>{{cite journal | vauthors = Weatherall M, Clay J, James K, Perrin K, Shirtcliffe P, Beasley R | title = Dose-response relationship of inhaled corticosteroids and cataracts: a systematic review and meta-analysis | journal = Respirology | volume = 14 | issue = 7 | pages = 983–990 | date = September 2009 | pmid = 19740259 | doi = 10.1111/j.1440-1843.2009.01589.x | s2cid = 43843511 }}</ref><ref name=Hod1995/> Corticosteroids most commonly cause posterior subcapsular cataracts.<ref name=Hod1995>{{cite journal | vauthors = Hodge WG, Whitcher JP, Satariano W | title = Risk factors for age-related cataracts | journal = Epidemiologic Reviews | volume = 17 | issue = 2 | pages = 336–346 | date = 1995 | pmid = 8654515 | doi = 10.1093/oxfordjournals.epirev.a036197 }}</ref> People with [[schizophrenia]] often have risk factors for lens opacities (such as diabetes, hypertension, and poor nutrition). Second-generation [[antipsychotic]] medications are unlikely to contribute to cataract formation.<ref>{{cite journal | vauthors = Uçok A, Gaebel W | title = Side effects of atypical antipsychotics: a brief overview | journal = World Psychiatry | volume = 7 | issue = 1 | pages = 58–62 | date = February 2008 | pmid = 18458771 | pmc = 2327229 | doi = 10.1002/j.2051-5545.2008.tb00154.x }}</ref> [[Miotics]]<ref>{{cite journal | vauthors = van den Brûle J, Degueldre F, Galand A | title = [Drug-induced cataracts] | language = fr | journal = Revue Médicale de Liège | volume = 53 | issue = 12 | pages = 766–769 | date = December 1998 | pmid = 9927876 | trans-title = Drug-induced cataracts }}</ref> and [[triparanol]] may increase the risk.<ref>{{cite web |url=https://www.nlm.nih.gov/cgi/mesh/2012/MB_cgi?mode=&term=Triparanol&field=entry |title=Triperanol |publisher=National Library of Medicine |work=MeSH |access-date=2013-02-06 |url-status=dead |archive-url=https://web.archive.org/web/20151222085138/http://www.nlm.nih.gov/cgi/mesh/2012/MB_cgi?mode=&term=Triparanol&field=entry |archive-date=2015-12-22 }}</ref>

===Post-operative===
Nearly every person who undergoes a [[vitrectomy]]—without ever having had cataract surgery—will experience progression of [[nuclear sclerosis]] after the operation.<ref>{{cite journal | vauthors = Almony A, Holekamp NM, Bai F, Shui YB, Beebe D | title = Small-gauge vitrectomy does not protect against nuclear sclerotic cataract | journal = Retina | volume = 32 | issue = 3 | pages = 499–505 | date = March 2012 | pmid = 22392091 | doi = 10.1097/IAE.0b013e31822529cf | s2cid = 31308270 }}</ref> This may be because the native vitreous humor is different from the solutions used to replace the vitreous (vitreous substitutes), such as [[Balanced salt solution#Surgical irrigation solutions|BSS Plus]].<ref>{{cite journal | vauthors = Kokavec J, Min SH, Tan MH, Gilhotra JS, Newland HS, Durkin SR, Grigg J, Casson RJ | title = Biochemical analysis of the living human vitreous | journal = Clinical & Experimental Ophthalmology | volume = 44 | issue = 7 | pages = 597–609 | date = September 2016 | pmid = 26891415 | doi = 10.1111/ceo.12732 | doi-access = free }}</ref> This may also be because the native vitreous humour contains [[ascorbic acid]] which helps neutralize oxidative damage to the lens and because conventional vitreous substitutes do not contain ascorbic acid.<ref>{{cite journal | vauthors = Donati S, Caprani SM, Airaghi G, Vinciguerra R, Bartalena L, Testa F, Mariotti C, Porta G, Simonelli F, Azzolini C | title = Vitreous substitutes: the present and the future | journal = BioMed Research International | volume = 2014 | pages = 351804 | year = 2014 | pmid = 24877085 | pmc = 4024399 | doi = 10.1155/2014/351804 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Shui YB, Holekamp NM, Kramer BC, Crowley JR, Wilkins MA, Chu F, Malone PE, Mangers SJ, Hou JH, Siegfried CJ, Beebe DC | title = The gel state of the vitreous and ascorbate-dependent oxygen consumption: relationship to the etiology of nuclear cataracts | journal = Archives of Ophthalmology | volume = 127 | issue = 4 | pages = 475–482 | date = April 2009 | pmid = 19365028 | pmc = 2683478 | doi = 10.1001/archophthalmol.2008.621 }}</ref> Accordingly, for phakic patients requiring a vitrectomy it is becoming increasingly common for ophthalmologists to offer the vitrectomy combined with prophylactic [[cataract surgery]] to prevent cataract formation.<ref>{{cite journal | vauthors = Jalil A, Steeples L, Subramani S, Bindra MS, Dhawahir-Scala F, Patton N | title = Microincision cataract surgery combined with vitrectomy: a case series | journal = Eye | volume = 28 | issue = 4 | pages = 386–389 | date = April 2014 | pmid = 24406418 | pmc = 3983625 | doi = 10.1038/eye.2013.300 }}</ref>

===Hyperbaric oxygen therapy===

[[Hyperbaric oxygen therapy]] (HBOT) is the administration of 100% oxygen at pressures greater than one-atmosphere absolute pressure (1 ATA) for a therapeutic purpose. HBOT can have several side effects, including the long-term development of cataracts. This is rare and generally associated with multiple HBOT exposures over a long period. As it does not usually become symptomatic during HBOT, it may often go unrecognised and is probably under-reported. Evidence is emerging that lifetime dosage of oxygen may be a precipitating factor in the development of age-related cataracts. Nuclear cataracts have been hypothesized to be the end stage of the far better known phenomenon of [[Hyperoxic myopia|hyperbaric myopic shift]].<ref name="Bennett and Cooper 2022" >{{cite journal |url=https://www.ncbi.nlm.nih.gov/books/NBK470454/ |website=www.ncbi.nlm.nih.gov |publisher=StatPearls Publishing LLC. |title=Hyperbaric Cataracts |first1=Michael H.|last1=Bennett |first2=Jeffrey S. |last2=Cooper |date=10 August 2022 |pmid=29261974 |access-date=27 February 2023 }}</ref>

===Other diseases===
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* [[Metabolic disease|Metabolic]] and nutritional diseases{{citation needed|date=September 2022}}
** [[Aminoaciduria]] or [[Oculocerebrorenal syndrome|Lowe's syndrome]]
** [[Cerebrotendineous xanthomatosis]]
** [[Diabetes mellitus]]
** [[Fabry's disease]]
** [[Galactosemia]] / [[galactosemic cataract]]
** [[Homocystinuria]]
** [[Hyperparathyroidism]]
** [[Hypoparathyroidism]]
** [[Hypervitaminosis D]]
** [[Hypothyroidism]]
** [[Hypocalcaemia]]
** [[Mucopolysaccharidoses]]
** [[Wilson's disease]]
* [[congenital cataract|Congenital]]
** [[Congenital syphilis]]
** [[Cytomegalic inclusion disease]]
** [[Rubella]]
** [[Cockayne syndrome]]
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* Genetic syndromes
** [[Down syndrome]]
** [[Patau syndrome]]
** [[Edwards syndrome]]
* Infections:
** [[Cysticercosis]]
** [[Leprosy]]
** [[Onchocerciasis]]
** [[Toxoplasmosis]]
** [[Varicella]]
* Secondary to other eye diseases:
** [[Retinopathy of prematurity]]
** [[Aniridia]]
** [[Uveitis]]
** [[Retinal detachment]]
** [[Retinitis pigmentosa]]
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[[File:Sunflower cataract.jpg|thumb|Sunflower cataract of a forty-year-old male with Wilson's disease and decompensated chronic liver disease]]
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