Colour vision deficiency can be classified as acquired or inherited. Inherited colour vision deficiency is primarily genetic, characterised by red-green colour blindness or defects in most cases. Acquired colour vision deficiency is often associated with pathological changes of retina or optic nerve, which may be caused by glaucoma or side effects of drugs.
Cases of total colour blindness are rare, and people with colour deficiency may not find it too inconvenient coping with everyday life. They can tell the differences by other signals, such as the positions or icons of traffic lights. However, their choices on occupation may be limited, particularly in the fields requiring colour perception like fine art, medicine, chemical engineering, electrical engineering and telecommunications.
When conducting a colour vision assessment, optometrists will use Ishihara test to screen red–green colour blindness or defects. More accurate colour test such as a Farnsworth D-15 test is needed in order to ascertain the severity of colour deficiency.