Colour Blindness

Labelled Diagram of the Eye

Labelled diagram of the structure of the retina

Colour Blindness is a general term used to indicate what is generally considered to be a deficiency in colour vision / perception. That is, people whose vision is affected by colour blindness do not perceive and distinguish colours in the same way as the vast majority of the population.

There are many specific conditions resulting in inability to distinguish certain colours from certain other colours. The term colour blindness may be applied to any (all) of these but it is usually helpful to use the most specific term known to be correct and likely to be understood by the person or audience to whom one is communicating.


Terms used to refer to specific forms of colour blindness, or issues concerning colour vision, include:

People who are dichromatic have "dichromacy", are called "dichromats", and can match any colour with some mixture of just two (2) wavelengths of light, whereas normally-sighted people are "trichromats", meaning that they need three (3) wavelengths of light in order to acceptably match any colour of light.

The three (3) forms of dichromacy are:

  • Protanopia - inability to distinguish between colours in the green-yellow-red section of the spectrum due to lack of long-wavelength sensitive retinal cones.
  • Deuteranopia - inability to distinguish between colours in the green-yellow-red section of the spectrum due to lack of medium-wavelength sensitive cones.
  • Tritanopia - inability to distinguish between the colours in the blue-yellow section of the spectrum.

The term Daltonism is also used to refer to "red-blindness" and is sometimes also used more generally (named after British Chemist, John Dalton 1766-1844).


Consider also unexpected (uncommon) sensations of specific colours.
Chromatopsia is the general term referring to abnormal colour vision in which objects appear to be abnormally/"falsely" coloured or tinged with a colour not perceived by most people. Some sources describe this as a form of colour blindness.

  • Chloropsia ("Green Vision") - a specific form of chromatopsia.
  • Cyanopsia ("Blue Vision") - a specific form of chromatopsia.
  • Xanthopsia ("Yellow Vision") - a specific form of chromatopsia.

Also compare colour blindness with other similar terms: night blindness, day blindness, snow blindness and blindness.

More about Ophthalmology:

This section includes short definitions of many diseases, disorders, and conditions of the eyes and visual system.
For definitions of other terms in this category, choose from the list to the left (but note that this is not a complete/exhaustive list).

Other related pages include

For further information see also our pages of books about ophthalmology.

The following books may also be of interest:

The Aging Eye (Harvard Medical School)
MCQ Companion to the Eye (Textbook)
The Secret of Perfect Vision: How You Can Prevent and Reverse Nearsightedness
What Your Doctor May Not Tell You About(TM) Glaucoma: The Essential Treatments and Advances That Could Save Your Sight

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