<unk>  vision deficiencies can be classified as acquired or inherited. * Acquired: Diseases, drugs (e.g., hydroxychloroquine), and chemicals such as styrene or organic solvents may cause<unk> . * Inherited: There are three types of inherited or congenital<unk>  vision deficiencies: monochromacy, dichromacy, and anomalous trichromacy. ;Monochromacy: also known as "total<unk> ", is the lack of ability to distinguish<unk> s (and thus the person views everything as if it were on a black and white television); caused by cone defect or absence. Monochromacy occurs when two or all three of the cone pigments are missing and<unk>  and lightness vision is reduced to one dimension. :;Rod monochromacy (achromatopsia): is an exceedingly rare, nonprogressive inability to distinguish any<unk> s as a result of absent or nonfunctioning retinal cones. It is associated with light sensitivity (photophobia), involuntary eye oscillations (nystagmus), and poor vision. :;Cone monochromacy: is a rare total<unk>  that is accompanied by relatively normal vision, electroretinogram, and electrooculogram. Cone monochromacy can also be a result of having more than one type of dichromatic<unk> . People who have, for instance, both protanopia and tritanopia are considered to have cone monochromacy. Since cone monochromacy is the damage of, or outright lack of, more than one cone in the retinal environment, having two types of dichromacy would be an equivalent. ;Dichromacy: is hereditary. Protanopia and deuteranopia are hereditary and sex-linked, affecting predominantly males. :;Protanopia: is caused by the complete absence of red retinal photoreceptors. Protans have difficulties distinguishing between blue and green<unk> s and also between red and green<unk> s. It is a form of dichromatism in which the subject can only perceive light wavelengths from 400 nm to 650 nm, instead of the usual 700 nm. Pure reds cannot be seen, instead appearing black; purple<unk> s cannot be distinguished from blues; more orange-tinted reds may appear as dim yellows, and all orange–yellow–green shades of too long a wavelength to stimulate the blue receptors appear as a similar yellow hue. It is present in 1% of males. :;Deuteranopia: affects hue discrimination in a similar way to protanopia, but without the dimming effect. Again, it is found in about 1% of the male population. :;Tritanopia: is a very rare<unk>  vision disturbance in which only the red and the green cone pigments are present, with a total absence of blue retinal receptors. Blues appear greenish, yellows and oranges appear pinkish, and purple<unk> s appear deep red. It is related to chromosome 7; thus unlike protanopia and deuteranopia, tritanopia and tritanomaly are not sex-linked traits and can be acquired rather than inherited and can be reversed in some cases. ;Anomalous trichromacy: is a common type of inherited<unk>  vision deficiency, occurring when one of the three cone pigments is altered in its spectral sensitivity. :;Protanomaly: is a mild<unk>  vision defect in which an altered spectral sensitivity of red retinal receptors (closer to green receptor response) results in poor red–green hue discrimination. It is hereditary, sex-linked, and present in 1% of males. In contrast to other defects, in this case the L‑cone is present but malfunctioning, whereas in protanopia the L‑cone is completely missing. :;Deuteranomaly: is caused by a similar shift in the green retinal receptors, and is by far the most common type of<unk>  vision deficiency, mildly affecting red–green hue discrimination in 5% of European males. It is hereditary and sex-linked. In contrast to deuteranopia, the green-sensitive cones are not missing but malfunctioning. :;Tritanomaly: is a rare, hereditary<unk>  vision deficiency affecting blue–green and yellow–red/pink hue discrimination. It is related to chromosome 7. In contrast to tritanopia, the S‑cone is malfunctioning but not missing. Genetics X-linked recessive inheritance Punnett squares for each combination of parents'<unk>  vision status giving probabilities of their offsprings' status, each cell having 25% probability in theory<unk>  is typically an inherited genetic disorder. It is most commonly inherited from mutations on the but the mapping of the human genome has shown there are many causative mutations – mutations capable of causing<unk>  originate from at least 19 different chromosomes and 56 different genes (as shown online at the Online Mendelian Inheritance in Man OMIM). Two of the most common inherited forms of<unk>  are protanomaly (and, more rarely, protanopia – the two together often known as "protans") and deuteranomaly (or, more rarely, deuteranopia – the two together often referred to as "deutans"). Both "protans" and "deutans" (of which the deutans are by far the most common) are known as "red–green<unk> -blind". They comprise about 8% of human males and 0.6% of females of Northern European ancestry. Some of the inherited diseases known to cause<unk>  are: * cone dystrophy * cone-rod dystrophy * achromatopsia(also called rod monochromatism, stationary cone dystrophy or cone dysfunction syndrome) * blue cone monochromatism(also called blue cone monochromacy or X‑linked achromatopsia) * Leber's congenital amaurosis * retinitis pigmentosa(initially affects rods but can later progress to cones and therefore<unk> . Inherited<unk>  can be congenital (from birth), or it can commence in childhood or adulthood. Depending on the mutation, it can be stationary, that is, remain the same throughout a person's lifetime, or progressive. As progressive phenotypes involve deterioration of the retina and other parts of the eye, certain forms of<unk>  can progress to legal<unk> , i.e. an acuity of 6/60 (20/200) or worse, and often leave a person with complete<unk> .<unk>  always pertains to the cone photoreceptors in retinas, as it is the cones that detect the<unk>  frequencies of light. About 8% of males, and 0.4% of females, are red–green<unk>  blind in some way or another, whether it is one<unk> , a<unk>  combination, or another mutation. Males are at a greater risk of inheriting an X‑linked mutation because males only have one X chromosome (XY, with the Y chromosome carrying altogether different genes from the X chromosome), and females have two (XX); if a woman inherits a normal X chromosome in addition to the one that carries the mutation, she will not display the mutation. Men do not have a second X chromosome to override the chromosome that carries the mutation. If 8% of variants of a given gene are defective, the probability of a single copy being defective is 8%, but the probability that two copies are both defective is Y male-only chromosome, neutral for green-red<unk> . X normal X chromosome. Xd X chromosome with a deficiency. XdG X chromosome with a deficiency of green. XdR X chromosome with a deficiency of red. Genotype Result X Y Unaffected man Xd Y Affected man X X Unaffected woman Xd X Carrier woman XdG XdR Carrier woman with 2 defective X XdG XdG or XdR XdR Affected woman Mother Father Daughter 1 Daughter 2 Son 1 Son 2 Affected Affectedsame<unk>  deficiency of mother Affected Affected Affecteddifferent<unk>  deficiency of mother Carrierwith 2 defective X Unaffected Carrier Carrierwith 2 defective X Affected Affected Carrierwith 2 defective X Unaffected Carrier Carrier Affectedsame<unk>  deficiency of mother Affected Carrier Affected Unaffected Affecteddifferent<unk>  deficiency of mother Carrierwith 2 defective X Unaffected Carrier Unaffected Unaffected Affected Carrier Unaffected Unaffected Unaffected Other causes Other causes of<unk>  include brain or retinal damage caused by accidents and other traumas which produce swelling of the brain in the occipital lobe, and damage to the retina caused by exposure to ultraviolet light (wavelengths 10 to 300 nm). Damage often presents itself later in life.<unk>  may also present itself in the range 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<unk> . Some subtle forms of<unk>  may be associated with chronic solvent-induced encephalopathy (CSE), caused by long-time exposure to solvent vapors. Red–green<unk>  can be caused by ethambutol, a drug used in the treatment of tuberculosis.
Color blindness
Flash blindness
Tunnel vision
Myopia
Cortical blindness
Amblyopia
Red eye 
Retinopathy