Colour blindness may be a hereditary condition or caused by disease of the optic nerve or retina. Acquired colour vision problems only affect the eye with the disease and may become progressively worse over time. Patients with colour blindness caused by disease usually have trouble discriminating blues and yellows.
Inherited colour blindness is more common, affects both eyes, and does not worsen over time. This type is found in about 8% of males and 0.4% of females, and is almost always passed down from mother to son.
Colour blindness may be partial (affecting only some colours), or complete (affecting all colours). Complete colour blindness is very rare. People who are completely colour blind often have other serious eye problems as well.
The symptoms of colour blindness are dependent on several factors, such as whether the problem is congenital, acquired, partial, or complete. The most common form involves difficulty distinguishing reds and greens. Difficulty distinguishing blues and greens is less common.
The symptoms of more serious inherited colour vision problems and some acquired types may include reduced vision, nystagmus, and the appearance of objects as shades of grey, which is very rare.
Colour vision deficiency is usually detected with special coloured charts called the Ishihara Test Plates. On each plate is a number composed of coloured dots. While holding the chart under good lighting, the patient is asked to identify the number. Once the colour defect is identified, more detailed colour vision tests may be performed.
There is no treatment or cure for colour blindness. People with mild colour deficiencies learn to compensate, by associating colours with certain objects, and they are usually able to identify colour as everyone else does. However, they are unable to appreciate colour in the same way as those with normal colour vision.