What color defects may be distinguished by the Ishihara test?

The Ishihara test is primarily designed to identify red and green color deficiencies. It consists of a series of plates, each showing a pattern of colored dots that form numbers or shapes that can be seen distinctly by individuals with normal color vision but are difficult or impossible for those with red or green color deficiencies to discern.

Red-green color deficiency is one of the most common forms of color vision deficiency, affecting a significant portion of the population, particularly males. This type of deficiency can be classified into two main categories: protanopia (difficulty seeing red) and deuteranopia (difficulty seeing green). The Ishihara test specifically targets these defects by using colors that exploit the differences in how individuals with normal color perception and those with red-green deficiencies perceive colors.

Identifying blue and yellow deficiencies is not the primary function of the Ishihara test, which is why options referring to those colors do not apply. While blue-yellow color deficiencies do exist, they are much rarer than red-green deficiencies and typically are not assessed in standard color vision tests like the Ishihara.