Colour vision deficiency (sometimes called colour blindness) represents a group of conditions that affect the perception of colour.
Most colour-blind individuals identify objects by their texture, shape and other features instead of their colour.
Types of Colour Vision Deficiency
- Red-green colour vision defects are the most common form of colour vision deficiency. Affected individuals have trouble distinguishing between some shades of red, yellow, and green.
- Blue-yellow colour vision defects, which are rarer, cause problems with differentiating shades of blue and green and cause difficulty distinguishing dark blue from black.
Red-green and blue-yellow forms of colour vision deficiency disrupt colour perception but do not affect the sharpness of vision.
- Blue cone monochromacy colour vision defects are less common and more severe.
Implications of Having a Colour Vision Defect
When colour vision deficiency is severe, the condition can have a significant impact on a person’s life. When the deficiency is mild, on the other hand, the symptoms may often go unnoticed until colour vision is tested.
- A colour vision deficiency can impair a person’s ability to read and interpret various diagrams and graphics such as maps, pie charts and slides used in presentations.
- Colour deficiency can also interfere with the interpretation of advertisements and graphics on websites.
- Colour deficient individuals may be prohibited from certain professions that involve being able to differentiate between colours. For example, careers in aviation, driving jobs and jobs that involve operating heavy machinery.
- Artistic or creative occupations involving interior design, painting, or even cooking may be difficult to pursue.
How It Runs in Families
- Colour blindness is a common hereditary condition which means it is usually passed down from your parents.
- Red/green colour blindness is passed from mother to son and is only found on the X chromosome.
How We Use the Ishihara Test as a Screening Tool
The Ishihara test is a colour perception test for red-green colour deficiencies. The tests consist of coloured plates, each of which contains a circle of dots appearing randomised in colour and size.
There are 24 plates:
Plates 1 – 17 each contain a number, plates 18 – 24 contain one or two wiggly lines. To pass each test you must identify the correct number, or correctly trace the wiggly lines.