Labelled Diagram of the Eye

Labelled diagram of the structure of the retina

Dichromatic is the adjective used to refer to deficiencies in colour vision in which those affected can perceive only two of the three primary colours. Those affected can match any colour with a particular combination of just two (2) wavelengths of light, whereas normally-sighted people need three (3) wavelengths of light in order to acceptably match any colour on the visible spectrum.

People who are dichromatic may be said to have "dichromacy". They are called dichromats.

There are three forms of dichromacy:

For comparison (in short summary):

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

See also more general information about colour 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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