Which tool is used to assess color vision?

The Ishihara plates are specifically designed to assess color vision, making them the correct choice for this question. These plates contain patterns of colored dots that form numbers or shapes that can only be seen by individuals with normal color vision. This method is widely recognized and used in clinical settings to diagnose color vision deficiencies, such as red-green color blindness, by presenting various tests that require the viewer to identify specific numbers or symbols among the colored dots.

In contrast, the Snellen chart is primarily used to measure visual acuity and is not designed for evaluating color perception. The Pellucid chart is not a standard tool in optometry for assessing color vision; it does not exist in the context of established vision tests. The Tono-pen is an instrument used to measure intraocular pressure to evaluate conditions like glaucoma and has no relevance to color vision assessment.

Thus, the reason the Ishihara plates are the correct choice lies in their specific purpose and effectiveness in diagnosing color vision disorders among patients.