Color Blindness 101

Color blindness, also called color vision deficiency, affects more than 10 million people in the United States alone. Up to 8% of the world’s male population is colorblind, while only 0.4% of those affected are women. The prevalence of color blindness varies by race, but researchers have more work to do to better understand how many people are affected.

The role of rods and cones

Rods and cones are cells found in the back of the eye. Think of the retina as the sensor in a digital camera. It is light sensitive and is responsible for the first steps in the process of seeing the world around us. The retina contains two types of light-sensitive cells—rods and cones. Rods outnumber cones in the retina and are responsible for our vision in very dim light. Cones are responsible for all daytime vision, including color vision.

Cones are sensitive to color

L cones, M cones, and S cones

There are 3 types of cone cells in the retina of humans. The scientific terms for these are L cones, M cones, and S cones. However, they are often referred to as “red” cones, “green” cones, and “blue” cones.

  • L cones respond to light with long wavelengths.
  • M cones respond to light with medium wavelengths.
  • S cones respond to light at short wavelengths.

In people with normal color vision, each different type of cone contains a different light-sensitive pigment, popularly referred to as red, green, and blue photopigments.

Color vision is based on comparisons between the light absorbed by the different types of cones. Color vision deficiency occurs when people are missing either the normal red or green photopigments. The most severe forms occur when all the cones that would normally contain red or green photopigment are missing red photopigment (protanopia) and/or they are missing green photopigment (deuteranopia). Less severe forms of color vision deficiency occur when three types of cones are present, but one cone is not functioning properly.

Most colorblind people do not see the world in just black and white. However, people with the most severe forms of color blindness are missing out on the vast majority of the colors that people with normal color vision see.

Tokyo Subway Map

Normal

Red/Green color-blind

Types of color vision deficiency

Anomalous Trichromacy

Protanomalous

  • Deep red colors appear dark
  • Missing normal red photopigment; however, two classes of cones have closely similar green pigments
  • Red and green components are missing from colors that have small amounts of either

Deuteranomalous

  • Brightness of colors is not affected
  • Missing normal green photopigment; however, two classes of cones have closely similar red pigments
  • Red and green components are missing from colors that have small amounts of either

Tritanomalous

  • Affects blue/green and yellow/red discrimination
  • Missing normal blue photopigment
  • Blue and yellow components are missing from colors that have small amounts of either

Dichromacy

Protanopia

  • All cones that would normally be red or green are green
  • No normal sensations of red or green
  • Deep red colors appear dark

Deuteranopia

  • All cones that would normally be red or green are red
  • No normal sensations of red or green

Tritanopia

  • Blue cones are missing
  • No normal sensation of blue or yellow

Monochromacy

Achromatopsia

  • Little or no cone function
  • Complete color blindness. Only able to perceive black, white, and shades of grey.
  • Poor visual acuity, extreme light sensitivity