Colour Vision Deficiencies

It is important to mention from the outset that most people diagnosed with a colour vision deficiency are very mild- Colour “BLINDNESS” is extremely rare. Mostly the individual would not have a problem naming colours, and may not confuse colours at all. However, they cannot appreciate subtle colour differences that a colour normal can- for example, think of all the different names there are for shades of colours, aqua, turquoise, navy, royal, deep, electric, to name just a few blues. A colour deficient person may just see “blue”, and wonder what everyone else is talking about.

Really the only difficulty a colour deficient person is likely to encounter are difficulties in being accepted into certain jobs where normal colour vision is deemed to be necessary- electronics, electrical, textiles, train drivers, pilots, firefighters, and most of the “forces”- Navy, Army, Air Force, Gardai.

There are various types of colour vision defects, but the most common are the congenital defects which affect red/green differentiation. Congenital (genetic) colour vision defects cannot be fixed, but equally will not deteriorate through life.

Classification

These deficiencies are classified Protan, if the individual has no red cone function, or has red cones which are less sensitive to the correct wavelength of light. Similarly Deutans have a problem with green, and Tritans have a difficulty with the shorter blue wavelengths. They can be further divided into those who have a mild to moderate defect- anomalous trichromats, who need the three primary colours in the mix to match the given colour. These individuals would be termed Protanomalous, Deuteranomalous, and Tritanomalous Trichromats.

The more severe colour deficiencies are usually due to a complete failure of the light sensitive pigments in one cone type- these dichromats can match any given spectral colour with a mixture of only 2 primary colours- that is they have a nearly complete insensitivity to one of the primary colours, red, green or blue. These subjects are similarly classified Protanopes, Deuteranopes and Tritanopes.

The most common colour vision defect is Deuteranomaly, where the individual is less sensitive to green. This would mean that to perceive the same colour as a normal, the deutan would require more green in the mix.

Whilst dichromats are rare, rarer still are the monochromats, which can match any colour with any other, just by adjusting its brightness. Even with poor colour discrimination, only a subset of these people would be termed truly colour blind.

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