How is Color Blindness Diagnosed

Color blindness can have a significant impact on a person’s life if not diagnosed early. In children, color perception issues can affect reading development and other learning abilities. Inherited color blindness is often difficult to diagnose in children. They may have no idea that they do not see colors correctly, and they may be able to identify the colors of familiar objects correctly simply through what they have learned.

Although there are a number of tests available to identify color vision defects, the most common is called the Ishihara or pseudoisochromatic plate test. The test was developed by Dr. Shinobu Ishihara in 1917. This test assesses for red/green color blindness, which is the most common form of color vision deficiency. During the test, the patient is asked to look at a series of circles comprised of colored dots and to identify the pattern, usually a number or letter, that is contained in the image. Individuals who are unable to make out the images are diagnosed with color blindness. Pediatric versions of the test that use simple objects and pictures are available for children who are not old enough to identify letters or numbers. In another test, the individual is asked to arrange a series of colored chips according to how similar they are in color. A person with a color vision deficit will be unable to arrange the chips in the correct order.

Color blindness may be a disqualifying medical condition for certain occupations that require the ability to differentiate between colors for safety reasons. For example, railway engineers need to be able to correctly distinguish between various signal lights. A lantern test is often used in vocational settings to determine the severity of the color vision deficit. The lantern has two red lights, two green lights, and a white light. The patient is asked to name the colors as the lights are shown in pairs.

The most accurate way to diagnose and determine the severity of color blindness is with an anomaloscope. This instrument was developed in the 20th century and is based on the color matching test developed by John William Strutt Rayleigh. The anomaloscope requires the individual to match two different light sources to the same color. The test is able to distinguish between different types of red/green color blindness. Some anomaloscopes are also able to test for blue/green color blindness.

Color vision tests should be a part of any complete eye examination. Experts recommend that children get at least one eye exam before starting school. Diagnosing color vision deficits early allows the child, with the help of parents and teachers, to develop coping mechanisms so that the learning process is not negatively affected.