Congenital or inherited defects are a genetic disorder. It usually affects only one type of cone, but can affect two or even all three of the cone types. The type of colour defect depends on which cones are affected. This affects both eyes, so the degree of colour defect in each eye is identical1.
Acquired colour vision defects on the other hand are caused by toxins, inflammation or detachment of the retina, macular degeneration, optic nerve diseases, and many other causes. These defects are not inherited, and so are not congenital. The problem usually occurs in all the cones and the central pathways from the eye to the brain. Usually the colour defect is red-green confusion or blue-yellow confusion. This type of colour vision defect can affect one or both eyes, and can have a different degree of colour defect in either eye1.
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