A non-specific term for congenital or acquired impairment of colour discrimination - usually reds and greens but can also be blues and yellows. It seems that more males are affected, with 7% of males showing this deficiency, compared to only about 0.5% of females. Colour vision deficiency is not a disease or degenerative condition, athough, occasionally, an acquired colour vision deficiency may be a symptom of other health problems. (Ref: Contact Lens Council)