color blind test
The different types of color blindness include red-green color blindness, blue-yellow color blindness, and complete color blindness.

Human eyes have two types of photoreceptors (cells that sense light and dark) in the retina (a sensory tissue layer that lines the inner surface of the back of the eyeball), namely, rods and cones.

  • Rods are sensitive to low light and detect light and dark, whereas cones are responsible for color perception and are sensitive to the different wavelengths of light.
  • There are three types of cones to identify various colors: S-cones (short wavelength for blue), M-cone (medium wavelength for green), and L-cones (long wavelength for red).

A person with normal color vision has trichromacy, which means a normal amount of all three cone types.

Depending on the type of cones that are deficient, color blindness may be of the following different types:

  • Red-green color blindness
    • A deficiency in green cones
      • Deuteranomaly: A shift in the color sensitivity of the green cones.
      • Deuteranopia: A complete lack of green cones.
    • A deficiency in red cones
      • Protanomaly: A shift in the color sensitivity of the red cones.
      • Protanopia: A complete lack of red cones.
  • Blue-yellow color blindness
    • A deficiency in blue cones
      • Tritanomaly: A shift in the color sensitivity of the blue cones.
      • Tritanopia: A complete lack of blue cones.
  • Complete color blindness
    • Dichromacy: Only two types of functioning cones are present.
    • Anomalous trichromacy: All three types of cones are present, but one of the cone types is unable to detect color normally.
    • Monochromacy or achromatopsia: Only one or none of the cones function normally.
    • Tetrachromacy: A rare condition that allows an enhanced type of color vision.

What is color blindness?

Color blindness is a common condition in which there is a decreased ability to see or differentiate between certain colors. This usually happens between shades of greens and reds and, occasionally, blues.

Color blindness can be inherited (present at birth) or acquired (a result of the aging process, eye disease or injury, and certain medications).

This condition affects males more often than females and is estimated to be found in approximately 1 in 12 men and 1 in 200 women in the world.

Color blindness is also called:

  • Color vision deficiency
  • Defective color vision

What causes color blindness?

There are several causes of color blindness including:

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What are the signs and symptoms of color blindness?

The symptoms of color blindness can range from mild to severe, including:

  • Trouble seeing or differentiating shades of colors
  • Inability to differentiate brightness of colors

In rare cases, people can see only in shades of gray called achromatopsia, which is a condition often associated with:

  • Nystagmus (rapid, uncontrollable eye movements)
  • Light sensitivity
  • Amblyopia (lazy eye)
  • Poor vision

How is color blindness diagnosed?

Based on the symptoms, the ophthalmologist will conduct simple tests to determine if a person has color blindness. 

  • Color vision test or Ishihara color test: Contains 38 plates of circles created by irregular colored dots in two or more colors.
  • Cambridge color test: Patients are told to find a “C” shape that is in a different color than the background on the computer screen.
  • Anomaloscope: Used to measure quantitative and qualitative anomalies in color perception.
  • Farnsworth-Munsell 100 hue test: Uses blocks or pegs of different shades of the same color.

Is color-blindness curable?

Currently, there are no medical treatments available for color blindness.

People with this condition learn to adapt and live with a relatively minor inconvenience. However, special glasses or corrective contact lenses may help people with red-green deficiency.

Treatment of the underlying medical condition may help resolve color vision deficiencies.

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Medically Reviewed on 11/29/2021
References
Image Source: iStock Images

Colour Blind Awareness. ·Colour Blindness. https://www.colourblindawareness.org/colour-blindness/

Huang M. Color blindness. Vision center. https://www.visioncenter.org/conditions/color-blindness/

Turbert D. What Is Color Blindness? American Academy of Ophthalmology. https://www.aao.org/eye-health/diseases/what-is-color-blindness

Seltman W. What Is Color Blindness? WebMD. https://www.webmd.com/eye-health/color-blindness

Medline Plus. Color vision deficiency. https://medlineplus.gov/genetics/condition/color-vision-deficiency/