The ability of the human eye to see colour is made possible by specific receptor cells in the retina of the back of the eye. These retinal receptor cells are known as “cones”. Unlike the other receptor cells (known as “rods”), the cones require more brightness for us to see, which is why we can see colours during the day or indoors in a well-lit room but we cannot perceive the colour of objects at night time or in a dark room.
There are three types of cones in the eye: one type detects red, one type detects green and one type detects blue. The three sets work together to give us the rich array of different colours that the human eye is able to perceive. Most people have normal colour vision but about 10% of men and 0.5% of women do not see some colours as well as the rest of the population. This deficiency in colour vision (often wrongly called “colour blindness”) is a result of one of the sets of cones being absent (known as “dichromacy”) from the eye or being less sensitive to light (known as “anomalous trichromacy”) than the other cones.
True colour blindness only occurs when all three sets of cones are absent from the eye. This is extremely rare and a test will reveal worse vision problems than just the colour blindness. While we have the facilities to detect this condition, our Vision Excellence optometrist has never encountered a patient with true colour blindness, either at Castle Hill or elsewhere.
Colour vision defects are usually of no major consequence. However, some of our Castle Hill patients, especially young men, have been referred to us because their colour vision status can have major restrictions on career options. For this reason, we have equipped our practice at Vision Excellence to identify and quantify any issues with colour vision so that our optometrist can assist with advice about vocational choices.