Colour blindness

What is it?

Colour blindness is the inability to distinguish differences between certain colours. The most common type is the red-green colour blindness, where red and green are perceived as the same colour.

What are the causes?

Colour blindness is an inherited condition that is sex-linked recessive. This means that females are the carriers of the colour blindness trait, but males are affected. As a result, very few women are colour blind, but approximately 1 in 10 men have some degree of colour blindness. Colour blindness is a malfunction of the retina, the light sensitive layer of the eye, which converts light energy into electrical energy that is then transmitted to the brain. This conversion is accompanied by two types of photoreceptor cells in the retina; rods and cones. The cones are responsible for encoding colour. Each cone contains structures or visual pigments sensitive to one of three wavelengths of light - red, green, and blue. Normal persons are able to match all colours of the spectrum by mixtures of only three fundamental colour sensitives. Hence, the huge variety of colours we perceive stem from the cone cells, response to different compositions of wavelengths of light.

What are the symptoms?

Symptoms may be so mild that affected people are unaware that they are colourblind unless specifically tested. Most commonly, people have difficulty distinguishing shades of a particular colour. Parents may notice colour blindness in a more severely affected child at the time the child would normally learn colours. In severe cases, other symptoms such as jiggling eyes (nystagmus) or roving eye movements may be present.

What are the types?

The most common form is red-green and has a wide range of variability within this group from very mild to extreme. The second most common form is the blue-yellow, and a red-green deficit is almost always associated with this form. The most severe form of colour blindness is achromatopsia, the inability to see any colour, and is often associated with other problems such as amblyopia (lazy eye), nystagmus, photosensitivity, and extreme poor vision.

How is the diagnosis made?

Several colour vision tests are available with your physician or eye specialist (Ophthalmologist). Testing for colour blindness is commonly performed along with other vision screenings. Usually isihara (pseudoisochromatic) plates are used to test colour vision. They are made of dot patterns composed of primary colours. These dot patterns represent a symbol that is superimposed on a background of randomly mixed colours. The test can determine certain abnormalities in a person’s colour vision.

What is the treatment?

There is no medical treatment for inherited colour blindness. Some acquired colour vision problems can be treated, depending on the cause. Colour blindness that is acquired may sometimes be improved by surgery. For example, if a person is having trouble seeing colours because of cataracts, surgery to treat the cataracts may improve colour vision. Also, colour vision may be improved if the problem is caused by a side effect of medication and that medication is stopped.Specially tinted contact lenses, eyeglasses, and glasses that block glare (with side shields or wide temples) are helpful because people with colour vision problems can see differences between colours better.

What are the complications?

Colour vision problem may limit a person’s career choices. For example, pilots, colour photographers, interior and clothing designers, and painters need normal colour vision. There are laws that prevent people with colour vision problems from holding certain jobs, such as airline pilot, police officer, and some positions in the military.

DoctorNDTV Team

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