These defects are due to partial or complete lack of light-sensitive photoreceptors (cones) in the retina, which is the layer of light-sensitive nerve cells lining the back of the eye. Cones help you to distinguish the colors red, green, and blue.

Most color vision problems that occur later in life are a result of disease, trauma, toxic effects from drugs, metabolic disease or vascular disease. Color vision defects from disease are less understood than congenital color vision problems. Disease-specific color blindness often affects both eyes differently, and the color vision defect usually gets worse over time. Acquired color vision loss can be the result of damage to the retina or optic nerve.

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