Editing Color blindness (section)

===Non-genetic causes===
Physical trauma can cause color blindness, either neurologically – brain trauma which produces swelling of the brain in the [[occiput|occipital lobe]] – or retinally, either acute (e.g. from laser exposure) or chronic (e.g. from [[ultraviolet light]] exposure).

Color blindness may also present itself as a symptom of degenerative diseases of the eye, such as [[cataract]] and age-related [[macular degeneration]], and as part of the retinal damage caused by [[diabetes]]. [[Vitamin A]] deficiency may also cause color blindness.<ref>
{{cite book
 |editor1-last=Leikin  |editor1-first=Jerrold B.
 |editor2-last=Lipsky  |editor2-first=Martin S.
 |year=2003
 |title=Complete Medical Encyclopedia  |edition=First
 |page=[https://archive.org/details/americanmedicala00amer/page/388 388]
 |publisher=Random House, for the American Medical Association
 |location=New York, NY
 |series=Random House Reference
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 |via=archive.org
 |url=https://archive.org/details/americanmedicala00amer
 |access-date=1 December 2011 |url-access=registration
}}
</ref>

Color blindness may be a [[side effect]] of prescription drug use. For example, red–green color blindness can be caused by [[ethambutol]], a drug used in the treatment of [[tuberculosis]].<ref>
{{cite web |last=Unknown |first=Unknown |title=NEI - Types of Color Vision Deficiency |url=https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/color-blindness/types-color-vision-deficiency |url-status=live |archive-url=https://web.archive.org/web/20140708223716/http://www.rxlist.com/myambutol-drug.htm |archive-date=2014-07-08 |access-date=2024-07-21 |website=www.nei.nih.gov |series=Color Blindness, Color Vision Deficiency |quote=Description, Types of Color Vision Deficiency,}}
</ref> Blue–yellow color blindness can be caused by [[sildenafil]], an active component of [[Viagra]].<ref>{{cite web
 |title=Viagra (Sildenafil Citrate) Drug
 |series=drug information
 |website=RxList.com
 |quote=Description, user reviews, drug side effects, interactions–prescribing information
 |url=http://www.rxlist.com/viagra-drug.htm
 |access-date=2022-06-03
 |archive-date=8 June 2022
 |archive-url=https://web.archive.org/web/20220608010719/https://www.rxlist.com/viagra-drug.htm
 |url-status=live
 }}</ref> [[Hydroxychloroquine]] can also lead to [[hydroxychloroquine]] retinopathy, which includes various color defects.<ref>{{cite book
 |last1=Fraunfelder
 |first1=Frederick T.
 |last2=Fraunfelder
 |first2=Frederick W.
 |last3=Chambers
 |first3=Wiley A.
 |year=2014
 |title=Drug-Induced Ocular Side Effects: Clinical ocular toxicology e‑book
 |page=79
 |publisher=Elsevier Health Sciences
 |isbn=978-0-323-31985-0
 |url=https://books.google.com/books?id=6bqXBAAAQBAJ&pg=PA79
 |language=en
 |access-date=19 March 2023
 |archive-date=3 October 2024
 |archive-url=https://web.archive.org/web/20241003080813/https://books.google.com/books?id=6bqXBAAAQBAJ&pg=PA79#v=onepage&q&f=false
 |url-status=live
 }}</ref> Exposure to chemicals such as [[styrene]]<ref>
{{cite journal
 |vauthors = Choi AR, Braun JM, Papandonatos GD, Greenberg PB
 |date = November 2017
 |title = Occupational styrene exposure and acquired dyschromatopsia: A systematic review and meta-analysis
 |journal = American Journal of Industrial Medicine
 |volume = 60 |issue = 11 |pages = 930–946
 |pmid = 28836685 |pmc = 5652067
 |doi = 10.1002/ajim.22766
}}
</ref> or organic solvents<ref>
{{cite journal
 |vauthors = Betancur-Sánchez AM, Vásquez-Trespalacios EM, Sardi-Correa C
 |date = January 2017
 |title = Impaired colour vision in workers exposed to organic solvents: A systematic review
 |journal = Archivos de la Sociedad Espanola de Oftalmologia
 |volume = 92 |issue = 1 |pages = 12–18
 |pmid = 27422480 |doi = 10.1016/j.oftal.2016.05.008
}}
</ref><ref name="Dick">
{{cite journal
 | last = Dick  |first = F.D.
 | date = March 2006
 | title = Solvent neurotoxicity
 | journal = Occupational and Environmental Medicine
 | volume = 63 | issue = 3 | pages = 221–6, 179
 | pmid = 16497867 | pmc = 2078137 | doi = 10.1136/oem.2005.022400
}}
</ref> can also lead to color vision defects.

Simple colored filters can also create mild color vision deficiencies. John Dalton's original hypothesis for his deuteranopia was actually that the [[vitreous humor]] of his eye was discolored:

{{Blockquote
|text=I was led to conjecture that one of the humours of my eye must be a transparent, but coloured, medium, so constituted as to absorb red and green rays principally... I suppose it must be the vitreous humor.
|author=John Dalton
|source=''Extraordinary facts relating to the vision of colours: with observations'' (1798)
}}

An autopsy of his eye after his death in 1844 showed this to be definitively untrue,<ref>{{cite journal |last1=Hunt |first1=D. |last2=Dulai |first2=K. |last3=Bowmaker |first3=J. |last4=Mollon |first4=J. |title=The Chemistry of John Dalton's Color Blindness |journal=Science |date=February 17, 1995 |volume=267 |issue=5200 |pages=984–988 |doi=10.1126/science.7863342|pmid=7863342 |bibcode=1995Sci...267..984H |s2cid=6764146 }}</ref> though other filters are possible. Actual physiological examples usually affect the blue–yellow opponent channel and are named [[Cyanopsia]] and [[Xanthopsia]], and are most typically an effect of yellowing or removal of the [[Lens (anatomy)|lens]].

The opponent channels can also be affected by the prevalence of certain cones in the [[retinal mosaic]]. The cones are not equally prevalent and not evenly distributed in the retina. When the number of one of these cone types is significantly reduced, this can also lead to or contribute to a color vision deficiency. This is one of the causes of '''tritanomaly'''.

Some people are also unable to distinct between blue and green, which appears to be a combination of [[Cultural neuroscience#Culture differences in visual stimuli|culture]] and exposure to UV-light.<ref>{{Cite journal |last1=Josserand |first1=Mathilde |last2=Meeussen |first2=Emma |last3=Majid |first3=Asifa |last4=Dediu |first4=Dan |date=2021 |title=Environment and culture shape both the colour lexicon and the genetics of colour perception |journal=Scientific Reports |language=en |volume=11 |issue=1 |pages=19095 |doi=10.1038/s41598-021-98550-3 |pmid=34580373 |pmc=8476573 |bibcode=2021NatSR..1119095J |issn=2045-2322}}</ref>