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photo:color_blindness

color blindness / color vision deficiency

see also:

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

types of colour blindness

Deutan color blindness

  • 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

Protan color blindness

  • 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

Tritan color deficiency

  • 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.

blue cone monochromatism

  • 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).

Achromatopsia

  • 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.

Other acquired forms of color vision deficiency

  • 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.
photo/color_blindness.txt · Last modified: 2019/04/04 05:06 by gary1