During color blindness tests, test administrators show patients multiple cards with dotted patterns, and patients must identify the number or symbol on the card, according to MedlinePlus. The cards generally contain primary colors and a superimposed number or symbol of a different color in the background.
Color blindness tests help doctors determine if a patient is unable to distinguish the difference between certain colors. Doctors perform color blindness tests in rooms with regular lighting, and testers are generally seated in a comfortable position and told to cover one eye, explains MedlinePlus. The card with the dotted pattern is held approximately 14 inches away from the tester's face before he is asked to identify the symbol. Test administrators may also ask patients to identify a color's intensity or describe the difference in a symbol's color when viewed from one eye compared to the other. A person who normally wears glasses would wear them during the color blindness test. Practitioners may also conduct a practice session on anxious children to make them more comfortable.
Color vision tests may be part of a routine eye exam, or an employer may order them to screen job applicants whose duties require them to perceive colors correctly, notes WebMD. Red-green color blindness, or the inability to tell the difference between red and green shades, is most common, according to MedlinePlus.