Colourblindness

Colourblindness is not a form of blindness at all, but a deficiency in the way you see colour. If you are colourblind, you have difficulty distinguishing certain colours, such as blue and yellow or red and green.

Colourblindness (or, more accurately, colour vision deficiency) is an inherited condition that affects males more frequently than females. According to Prevent Blindness, an estimated 8% of males and less than 1% of females have colour vision problems.

Red-green colour deficiency is the most common form of colourblindness.

Much more rarely, a person may inherit a trait that reduces the ability to see blue and yellow hues. This blue-yellow colour deficiency usually affects men and women equally. Do you have difficulty telling if colours are blue or yellow, or red or green? Do people sometimes inform you that the colour you think you're seeing is wrong?

If so, these are primary signs that you have a colour vision deficiency. Contrary to popular belief, it is rare for a colourblind person to see only in shades of gray.

Most people who are considered "colourblind" can see colours, but certain colours appear washed out and are easily confused with other colours, depending on the type of colour vision deficiency they have. Colourblindness occurs when light-sensitive cells in the retina fail to respond appropriately to variations in wavelengths of light that enable people to see an array of colours.

Photoreceptors in the retina are called rods and cones. Rods are more plentiful (there are approximately 100 million rods in the human retina) and they are more sensitive to light than cones, but rods are incapable of perceiving colour.

The 6 million to 7 million cones in the human retina are responsible for colour vision, and these photoreceptors are concentrated in the central zone of the retina called the macula.The center of the macula is called the fovea, and this tiny (0.3 mm diameter) area contains the highest concentration of cones in the retina and is responsible for our most acute colour vision.

Inherited forms of colourblindness often are related to deficiencies in certain types of cones or outright absence of these cones.

Cataracts: Clouding of the eye's natural lens that occurs with cataracts can "wash out" colour vision, making it much less bright. Fortunately, cataract surgery can restore bright colour vision when the cloudy natural lens is removed and replaced with an artificial intraocular lens.

Certain medications: For example, an anti-seizure drug called tiagabine has been shown to reduce colour vision in about 41% of those taking the drug, although effects do not appear to be permanent.

Leber's hereditary optic neuropathy (LHON): This type of inherited optic neuropathy can affect even carriers who don't have other symptoms but do have a degree of colourblindness. Red-green colour vision defects primarily are noted with this condition.

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Sarah Rose
Journal Manager Journal of Eye Diseases and Disorders
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