|Vision and EyeCare FAQ|
Section 7: Colour Vision Problems
7.1 Defective Colour Vision:
Defects in colour vision, often incorrectly referred to as colour "blindness" fall into two main categories:
(a) Congenital Colour Vision Defects
(b) Acquired Colour Vision Defects
The distinction between the two varieties are that acquired defects are often the result of some disease process which affects the colour vision receptors or higher neural pathways. Congenital colour vision defects are genetically related.
7.2 Classification of Congenital Colour Vision Defects
Colour vision defects are classified via the number of primary spectral colours which an individual requires to match any other spectral colour. The normal individual usually requires 3 primaries and is classified as a trichromat.
(a) Achromatic (Monochromatic) Colour Vision
+ no colour vision
+ only light - dark discrimination
+ lack of retinal function (typical case)
+ higher centre defects (generally atypical)
(b) Dichromatic Colour Vision
+ colour distinctions of 2 kinds (achromatic or R-G/Y-B)
+ 4 types
- protanopia and deutranopia (confusion of colours from green through yellow to red)
- tritanopia and tetartanopia (confusion of colours from blue through green to yellow.
(c) Trichromatic Colour Vision
+ anomalous type requires 3 stimulus primaries to match stimuli but matches are outside the normal range
+ 3 types - protan, deutran, tritan
The colour defective person has difficult in distinguising colours that are on "confusion lines". For example, protanopes confuse blue-greens (and greys) with red (and browns). The deutranopes make mistakes with blue-greens and purple. While tritanopes confuse yellow with violet. The last dichromat group; tetartanopes, confuse yellow with blue. The anomalous types have difficulty with light tints and dark shades.
Colour defective vision is inherited as a sex-linked recessive characteristic. It is more common in men than women. The most common defect is deutranomoly with an incidence of 5% or males, protanomaly affects 1.5% and protanopia and deutranopia about 1% each.
7.3 Classification of Acquired Colour Vision Defects
Acquired colour vision problems can be the result of lesions of the macula, optic nerve, or visual cortex. Also changes in the optical media, eg cataract changes, or toxic effects of chemicals can alter colour perception.
Acquired colour vision defects are generally asymmetrical in the two eyes, eg affecting red-green as well as yellow-blue, while also there may be other defects of visual function ( visual field defects).
7.4 WWW Resource on Colour
Poynton's GammaFAQ and ColorFAQ (updated 1997-02-27)
© Grant Sayer , email: firstname.lastname@example.org
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