Colour Testing

A colour vision deficiency is usually classified as a mild disability; however there are some occupations that you cannot pursue if you have a colour vision defect.

A colour vision deficiency sometimes called Colour blindness, is the inability or decreased ability to see colour, or perceive colour differences, under normal lighting conditions. Colour vision deficiency affects a significant percentage of the population. The most usual cause is a fault in the development of one or more sets of retinal cones that perceive color in light and transmit that information to the brain. This type of colour vision deficiency is usually a sex-linked condition. The genes that produce photo pigments are carried on the X chromosome; if some of these genes are missing or damaged, a colour vision deficiency will be expressed in males with a higher probability than in females because males only have one X chromosome, whereas females have two and a functional gene on only one of the X chromosomes is sufficient to yield the necessary photo pigments. Therefore only about 0.5% of females are affected by this condition while about 9% of males are affected.

Color blindness can also be produced by physical or chemical damage to the eye, the optic nerve, or parts of the brain. However this is very rare.

At Evans & McMahon Eyecare Plus we will normally screen all children for colour vision defects, however if you have a family history of colour vision defects and/or need to have an occupational test for a colour vision defect please talk to the optometrist about testing. We have a number of tests which help to differentiate the type and severity of colour vision defects.