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Eye Health Library / Eye Exam & Diagnoses
Colour deficiency occurs when your ability to distinguish colours and shades is different than normal. The term colour blindness is often used, but usually incorrectly. Only a very small number of people are completely unable to identify any colours, a condition called achromatopsia. Colour deficiency is more common in males than females, with one in 10 males having a colour deficiency.
Colour deficiency is usually an inherited condition, passed from mother to son, but it can also result from certain diseases, trauma or as a side effect of certain medications. Colour deficiency is the result of an imbalance in the three kinds of cones in the retina that allow us to perceive colour.
There are three types of colour deficiency: two different kinds of red-green deficiency and one called blue-yellow deficiency. The red-green deficiencies are by far the most common and are usually inherited, resulting in the inability to distinguish between certain shades of reds, browns, pinks and oranges, or greens and blues. Blue-yellow deficiency is very rare and is usually acquired secondary to damage to the optic nerve and results in the inability to distinguish between certain shades of blue, as well as shades of yellow. People with complete colour blindness see objects in shades of black, white and grey.
Children who are colour deficient are generally unaware of their condition. They assume that everyone sees things the way they do. As a result, a complete optometric examination, including a test for colour vision, is recommended for every child. The test for colour deficiency is a relatively simple one, typically involving the viewing of a series of coloured plates with numbers or designs. The plates have been created in such a way that a person with normal colour vision can see certain figures in the designs. A person with a colour deficiency will either see a different number of designs or will be unable to distinguish the figures.
Every child should be checked for colour deficiency by at least age five. It is important to detect colour deficiency early because colour coded learning materials are used extensively in the primary grades. In addition, colour deficiency may affect the career path of an individual, since the ability to distinguish colours is an important aspect of some jobs, such as pilots, electricians, some military personnel, police officers and others.
Unfortunately, a cure for colour deficiency has not yet been discovered. A person with a colour deficiency can, however, be taught proper colour naming and to accurately distinguish colours. For example, you can be taught to recognize the brightness and location of a traffic light rather than the colour itself. It is sometimes possible to increase the ability to distinguish colours with the use of special filters.