Assessment of Color Vision

Defects in color vision may be classified as congenital or acquired. Congenital defects are more common and refer to a color vision deficiency that is inherited and therefore is present at birth. Congenital color vision deficiencies most often affect males. Acquired defects refer to a color vision deficiency that is acquired after birth, resuiting from such factors as an eye injury, disease, and certain drugs. Color vision tests, such as the Ishihara test (Figure), detect congenital color vision disturbances and are commonly performed in the medical office. A basic screening for color vision can be performed by asking the patient to identify the red and green lines on the Snellen eye chart.

Figure.Ishihara color plates. Polychromatic plates. In the upper figure the normal person reads 74, but the red-green color-blind person reads 21. In the lower figure the red-blind person (protanope) reads 2, but the green-blind person (deuteranope) reads 4. The normal-vision person reads 42. Note that reproduced plates are not good to test for color deficiency. (From Ishihara J: Tests for colorblindness, Tokyo, 1920, Kanehara.)