The retina is the light-sensitive layer of nerves at the back of the eye that sends signals to the brain, allowing us to see. The retina is associated with other areas of the eye, like the macula, fovea, rods, and cones. Cone cells, which are concentrated in the macular, are responsible for our ability to see color.
Our eyes have about 6 million cones cells. Of these cells, there are three types: red-sending, green-sensing, and blue-sensing. Each cone type is sensitive to different wavelengths of visible light. Light reflected off objects stimulates different cones, which are then sent as signals along the optic nerve to the brain and are interpreted as distinct colors.
Colour deficiency occurs when one or more of these cells are missing, aren’t working, or detect color differently than they should.
There are varying severities of color deficiency. The mildest form means people can’t detect color differences in low light but can see colors well in good light. The most severe form is when everything is shades of grey. The most common type of color deficiency is the inability to see some shades of red and green.
Most of those with color deficiency inherit it, and the condition remains stable throughout one’s life. However, some eye diseases and health conditions can cause a sudden change in color perception and requires an immediate visit to an optometrist to be checked.
Color deficiency is easily diagnosed during a comprehensive eye exam with an Ishihara color test. You’ll be given a series of images with dots and lines and asked to distinguish the numbers. If you’re at home and curious if you may be color blind, you can take a quick test online. However, online tests do not replace the professional opinion of your optometrist.