What is colour deficiency?

Colour deficiency occurs when your ability to distinguish certain colours and shades is less than normal. The term "colour blind" is often used, but usually incorrectly. Only a very small number of people are completely unable to identify any colours.  Congenital deficiencies result from an inborn abnormality of the cone photoreceptors.  There are three types—dichromacy (protanopia, deuteranopia, tritanopia), anomalous trichromacy, and rod monochromacy. Red-green deficiency (protanopia & deuteranopia) is by far the most common and results in the inability to distinguish certain shades of red and green. Blue-yellow deficiency (tritanopia)is less common and affects the perception of blue and yellow colours. In very rare cases, colour deficiency exists to an extent that no colours can be detected (rod monochromacy). This person sees all things in shades of black, white and gray and matches hues based on brightness.

There are different methods of testing colour vision which is generally used during routine visual assessments.  Colour vision can be altered due to injuries, cataracts, and macular degeneration.


Dr. Patricia Fink


Millcroft Shopping Centre
2080 Appleby Line, Unit E6
Burlington, Ontario, L7L6M6
Tel: (905) 319-1066