Visual impairments

Monochromacy

(Monochromatic vision, Achromatopsia)

A type of vision where sensory input is provided by only one type of photoreceptor or pigment. Typically used to refer to specific types of color vision deficiencies.

Scotopic vision

An aspect of normal vision under low-light conditions, where the rods are the only operating photoreceptors.

Example image simulating scotopic (rod-only) monochromacy. Example image simulating scotopic (rod-only) monochromacy.

Achromatopsia (rod monochromacy)

An inherited color vision deficiency that causes extreme light sensitivity (day blindness), and a loss of visual acuity and color discrimination.

Achromatopsia is very rare and affects 0.00003% - 0.00002% of people.

Example image simulating achromatopsia with full loss of color discrimination, lowered visual acuity, and light sensitivity. Example image simulating achromatopsia with full loss of color discrimination, lowered visual acuity, and light sensitivity.

Blue cone monochromacy

An inherited color vision deficiency where the red (LWS) and green (MWS) cones have loss of functionality. It causes extreme light sensitivity (day blindness), and a loss of visual acuity and color discrimination.

It is difficult to distinguish blue cone monochromacy from achromatopsia. Blue cone monochromacy is very rare and affects 0.00001% of people.

Example image simulating blue cone monochromacy with full loss of color discrimination, lowered visual acuity, and light sensitivity. Example image simulating blue cone monochromacy with full loss of color discrimination, lowered visual acuity, and light sensitivity.

Cerebral achromatopsia

A type of color vision deficiency that can be the result of missing cone pigments. Cerebral achromatopsia is a type of monochromacy resulting from stroke or damage to areas of the brain.

Example image simulating cerebral achromatopsia, where all cones & rods transmit signals but the brain cannot discern color. Example image simulating cerebral achromatopsia, where all cones & rods transmit signals but the brain cannot discern color.

How it affects UI design

Designing with color vision deficiencies in mind is important. Most issues can be resolved by compliance with WCAG 1.4.1 (use of color) and 1.4.3 (contrast minimum).

Most tools improperly simulate types of monochromacy, as they fail to account for increased light sensitivity (which affects contrast sensitivity and discrimination). Consider personalization settings to give users the ability to adjust contrast to meet their needs.

Supporting Windows high contrast mode will help users with monochromacy and light sensitivity.

Sources:

  1. R.W.G. Hunt, M.R. Pointer (2011). Measuring Colour. John Wiley & Sons, Inc. Pages 443
  2. Daniel Flück. Types of color blindness. Colblindor. https://www.color-blindness.com/types-of-color-blindness/
  3. Daniel Flück. Monochromacy: complete color blindness. Colblindor. https://www.color-blindness.com/2007/07/20/monochromacy-complete-color-blindness/
  4. Achromatopsia. Fighting Blindness. https://www.fightingblindness.org/diseases/achromatopsia
  5. Andrew Somers. Color vision deficiency simulator. Myndex Research. https://www.myndex.com/CVD/
  6. BCM. BCM Families Foundation. https://www.blueconemonochromacy.org/blueconemonochromacy/
  7. Blue cone monochromatism. National Institute of Health (Genetic and Rare Diseases Information Center). https://rarediseases.info.nih.gov/diseases/917/blue-cone-monochromatism
  8. Cerebral achromatopsia. Wikipedia. https://en.wikipedia.org/wiki/Cerebral_achromatopsia
  9. Scotopic vision. Wikipedia. https://en.wikipedia.org/wiki/Scotopic_vision