<unk> <unk>  vision deficiency) is the decreased ability to see<unk>  or differences in<unk> . It can impair tasks such as selecting ripe fruit, choosing clothing, and reading traffic lights.<unk>  may make some educational activities more difficult. However, problems are generally minor, and most<unk> -blind adapt. People with total<unk>  (achromatopsia) may also be uncomfortable in bright environments and have decreased visual acuity. The most common cause of<unk>  is an inherited problem in the development of one or more of the three sets of the eyes' cone cells, which sense<unk> . Among humans, males are more likely to be<unk>  blind than females, because the genes responsible for the most common forms of<unk>  are on the X chromosome. This genetic fault is passed on in what's known as an X-linked inheritance pattern. Females have two X chromosomes, so a defect in one is typically compensated for by the other. Non-color-blind females can carry genes for<unk>  and pass them on to their children. Males only have one X chromosome and therefore always express the genetic disorder if they have the recessive gene.<unk>  can also result from physical or chemical damage to the eye, the optic nerve, or parts of the brain. Diagnosis is typically with the Ishihara<unk>  test; other methods include genetic testing. There is no cure for<unk> . Diagnosis may allow a person's teacher to change the teaching method to accommodate the condition. Special lenses such as X-chrome lenses may help people with red–green<unk>  in bright light. Mobile apps can help people identify<unk> s. Red–green<unk>  is the most common form, followed by blue–yellow<unk>  and total<unk> . Red–green<unk>  affects up to 8% of males and 0.5% of females of Northern European descent, which means around 1 in 12 men and 1 in 200 women. The ability to see<unk>  also decreases in old age. In certain countries,<unk>  may make people ineligible for certain jobs, such as those of aircraft pilots, train drivers, crane operators, and people in the armed forces. The effect of<unk>  on artistic ability is controversial. The ability to draw appears to be unchanged, and a number of famous artists are believed to have been<unk>  blind.
Color blindness
Flash blindness
Tunnel vision
Myopia
Cortical blindness
Amblyopia
Red eye 
Retinopathy