People with normal color vision have the ability to perceive a million different colors. This is due to the presence of three types of cone photoreceptors in our retina that send color messages to our brain. Each of these cones has a different sensitivity to light of different wavelengths, and for this reason are referred to as “blue,” “green,” and “red,” or, more appropriately, short (S), medium (M), and long (L) wavelength cones. This nomenclature implies that the specific cone provides color information for the wavelength of light that excites it best. A person with normal color vision is said to be a trichromat, a term that implies having the three sets of cone photoreceptors.
Color blindness means one has a faulty cone or two which can greatly decrease color perception. A color blind person may have difficulty seeing the difference between colors, how bright the colors are, and different shades of colors. Sometimes the symptoms are so mild that one may not notice them. Many color blind people do not know that they have it as they have gotten used to the way they see colors. People with very serious cases of color blindness might have other symptoms like wobbly eyes (nystagmus) and light sensitivity.
Normal color vision is known as trichromacy. It means one has all the types of cone photoreceptors: blue, green, and red. When one type of cone is non-functional or not present, one becomes a dichromat, or color blind. There are several types, depending on which cones are deficient.
The most common form, red-green color blindness is actually a group of two very similar subset of color deficiencies.
Protanomaly is a reduced sensitivity to red light due to defective red cones. Complete absence of the red cones is called Protanopia. This subset of color blind patients has difficulty distinguishing between red and green, and appreciate more green. As a consequence, the patient finds red, orange, yellow and green difficult to distinguish from each other, as they all appear very similar.
The other subset is called deuteranomaly, when one has a reduced sensitivity to green light due to defective green cones. Complete absence of the green cones is called deuteranopia. These patients find it difficult to distinguish between green and warm colors such as yellow, orange, red and brown (they all look similar).
In red-green color blindness, patients find it difficult to distinguish between blue and violet and pink and gray. Blues and yellows stand out.
This form of color blindness is brought about by having defective blue cones and is called tritanomaly. Complete absence of the blue cone is tritanopia. Both are extremely rare. Affected patients find it difficult to distinguish blue from green (appreciating more green), as well as yellow from violet (appreciating more violet).
Patients with a deficiency in all 3 types of cone photoreceptors will have a monochromatic vision and is called monochromacy. Complete absence of all types of cone photoreceptors is achromatopsia. One can imagine them seeing the world in black and white.
Most color blind people at birth are men because the genes responsible for the cone deficiency is inherited from the X chromosome of the mother. One is also more likely to acquire color blindness if you have certain chronic eye diseases (glaucoma, age-related macular degeneration), or chronic illness (diabetes), or take certain medicines for a long time.
A color vision test can be done for anyone 5 years old or older. It can be done by using either a color plate test or a hue discs.
There is no cure for color blindness, but if one is having problems with everyday tasks, there are devices that can help.
The first pair of commercially available special glasses for the color blind was released in 2012. At the moment there is a wide selection of frame shapes that contain lenses for the specific type of color blindness. Special contact lenses (metasurface-based) are still undergoing clinical trials.
- Purves, D., Augustine, G., Fitzpatrick, D., et al editors. (2001). Neuroscience, 2nd edition.
Videos | Color Blindness