Which of the following is NOT true regarding Ishihara testing?

Ishihara testing is primarily designed to identify red-green color deficiencies, particularly by utilizing a series of colored plates that contain patterns discernible to individuals with normal color vision, but not to those with certain types of color blindness.

The correct answer identifies a statement that is not true about Ishihara testing: it does not effectively distinguish between a deuteranope (someone who cannot perceive green) and a deuteranomalous trichromat (someone who has a milder form of green deficiency). This is due to the nature of the test, which focuses on detecting the presence of color vision deficiencies rather than differentiating between the subtleties of those deficiencies.

In contrast, the other statements regarding Ishihara testing highlight its utility and validity in clinical assessment. The test can certainly differentiate between a deuteranope and a protanope, as each will perceive the Ishihara plates differently, and it is particularly useful for diagnosing red-green deficiencies, which is its primary application. Furthermore, since Ishihara plates are made to take advantage of perceived color differences while using colored dots, it falls under the category of Pseudoisochromatic plate testing, a widely recognized method for evaluating color vision.