They do not measure the degree of deviation. For the diagnosis of deviant color perception another test is necessary, a quantitative test in form of small caps with color surfaces in all colors of the spectrum. The diagnosis of color deficiency should never be based on a screening test. If a child seems to have any confusion with colours, colour vision should be examined carefully. We have two eyes but see only one picture, image .
Visual information coming from the two eyes is fused into one image in the visual cortex .
Not all normally sighted have binocular vision . They do not use both eyes simultaneously, together. Some persons look alternatingly with their right or left eye. They are usually unaware that they use their eyes separately. It does not disturb them.