Color blindness
Other names	Color vision deficiency[1]
Example of an Ishihara color test plate. Viewers with normal color vision should clearly see the number "74". Viewers with red-green color-blindness will likely see the number "21".
Specialty	Ophthalmology
Symptoms	Decreased ability to see colors[2]
Duration	Long term[2]
Causes	Genetic (inherited usually X-linked)[2]
Diagnostic method	Ishihara color test[2]
Treatment	Adjustments to teaching methods, mobile apps[1][2]
Frequency	Red–green: 8% males, 0.5% females (Northern European descent)[2]

Color blindness or color vision deficiency (CVD) is the decreased ability to see color, differences in color, or distinguish shades of color.^[2] The severity of color blindness ranges from mostly unnoticeable to full absence of color perception.

Color blindness is usually a sex-linked inherited problem or variation in the functionality of one or more of the three classes of cone cells in the retina, which mediate color vision.^[2] The most common form is caused by a genetic condition called congenital red–green color blindness (including protan and deutan types), which affects up to 1 in 12 males (8%) and 1 in 200 females (0.5%).^[3] The condition is more prevalent in males because the opsin genes responsible are located on the X chromosome.^[2] Rarer genetic conditions causing color blindness include congenital blue–yellow color blindness (tritan type), blue cone monochromacy, and achromatopsia. Color blindness can also result from physical or chemical damage to the eye, the optic nerve, parts of the brain, or from medication toxicity.^[2] Color vision also naturally degrades in old age.^[2]

Diagnosis of color blindness is usually done with a color vision test, such as the Ishihara test. There is no cure for most causes of color blindness; however, there is ongoing research into gene therapy for some severe conditions causing color blindness.^[2] Minor forms of color blindness do not significantly affect daily life and color blind people automatically develop adaptations and coping mechanisms to compensate for the deficiency.^[2] However, diagnosis may allow an individual, or their parents/teachers, to actively accommodate the condition.^[1] Color blind glasses may help the red–green color blind at some color tasks,^[2] but they do not grant the wearer "normal color vision" or the ability to see "new" colors.^[4] Some mobile apps can use a device's camera to identify colors.^[2]

Depending on the jurisdiction, color blind people are ineligible for certain careers,^[1] such as aircraft pilots, train drivers, police officers, firefighters, and members of the armed forces.^[1][5] The effect of color blindness on artistic ability is controversial,^[1][6] but a number of famous artists are believed to have been color blind.^[1][7]