color blindness / color vision deficiency

Introduction

among populations with Northern European ancestry, 8% of males and around 1% of females have some degree of color blindness
it is usually discovered after formal testing with Ishihara Plates, although there are online digital alternatives
The OPN1LW and OPN1MW genes (responsible for red and green cones respectively) are located on the X chromosome, whereas the OPN1SW for blue cones is on a different autosomal chromosome
people with typical color vision can see about 1 to 7 million distinct colors.
those with deutan or protan color blindness may see only about 10% of those colors, however, those with mild forms can improve their color vision by either:
- buy glasses (such as those from Enchroma) which selectively filter out a narrow range of light wavelengths which reduce the overlap between red and green cones, however, a study showed that the glasses introduce a variation of the perceived color, but neither improve results in the diagnosis tests nor allow the observers with CVD to have a more normal color vision. ¹⁾
- use computer software to adjust the computer displays
  - Apple iOS has a colour filter setting under Settings: Accessibility: Display Accommodations which may help
  - Windows, Settings, Ease of Access, Color Filters
  - Daltonize for Google Chrome

a form of red-green color blindness characterized by the shifting of green light-sensitive M cone cells closer to red-sensitive cells than is normal, and are too sensitive to yellows, oranges, and reds
This causes “green-deficient” color blindness
greens, yellows, oranges, reds, and browns may appear similar, especially in low light.
it can also be difficult to tell the difference between blues and purples, or pinks and grays and they miss seeing all the range of pinks and purples in sunsets
in descendants of northern Europeans, 6% of males, 0.4% of females have this milder form Deuteranomaly which is inherited in an X-linked recessive manner
- a study of Ethiopian school children showed 2% of boys and ~0.4% of girls were deutan ²⁾
in addition, 1% of males have no green receptors Deuteranopia so greens look like dark purples

a form of red-green color blindness characterized by the shifting of red light-sensitive L cone cells closer to green-sensitive cells than is normal.
the red cones are not absent but do not detect enough red and are too sensitive to greens, yellows, and oranges
This causes “red-deficient” color blindness
greens, yellows, oranges, reds, and browns may appear similar, especially in low light. Red and black might be hard to tell apart, especially when red text is against a black background.
1% of males, 0.01% of females have this milder form - Protanomaly
in addition, ~1% of males have no red receptors Protanopia so reds look like dark greens

most commonly acquired later in life due to aging of the eye or medical complications.
It is characterized by a reduction in the sensitivity of the blue light-sensitive S cones such that blue shades seem darker and less vibrant.
it generally causes very poor visual acuity and severely reduced color vision
In extremely rare cases (1 in 100,000 people), tritanopia can be inherited in AD manner ³⁾
can cause confusion between blue versus green and red from purple.

this is a rare condition in which both the red and green cones are defective and as the genes for these are on the X chromosome, it is a X-linked recessive condition ⁴⁾
symptoms may include impaired color vision, low visual acuity (clarity or sharpness), photophobia (light sensitivity), myopia (nearsightedness), and nystagmus (fast, uncontrollable movements of the eye).

also known as “complete color blindness”
it is the only type that fully lives up to the term “color blind”
extremely rare
the most common underlying genetic mutations are autosomal recessive changes in CNGA3, CNGB3, GNAT2, PDE6H, PDE6C, or ATF6 genes
those who have achromatopsia only see the world in shades of grey, black and white.
The evidence to date suggests that gene therapy for achromatopsia will need to be applied early in childhood to be effective ⁵⁾
in some cases low vision disorders such as progressive cone dystrophy can cause a gradual deterioration of color vision that eventually turns into complete achromatopsia.

acquired color vision deficiency occurs as the result of ocular, neurologic, or systemic disease ⁶⁾
it may be a side effect of certain drugs, such as chloroquine, or result from exposure to particular chemicals, such as organic solvents.

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