What test is used to detect impaired color vision?

The Ishihara color test is specifically designed to detect color vision deficiencies, making it the appropriate choice for assessing impaired color vision. This test involves a series of plates with colored dots that form numbers or shapes that can typically be seen by those with normal color vision but are often indistinguishable for individuals with color blindness.

The Snellen chart is utilized for measuring visual acuity and determines how well a person can see at a distance, rather than assessing color perception. Ophthalmoscopy allows healthcare providers to examine the interior structures of the eye, including the retina and optic nerve, but does not evaluate color vision specifically. Tonometry measures intraocular pressure to assess for conditions like glaucoma, and it does not provide information about a person's ability to perceive color.

Thus, the Ishihara color test is uniquely suited for diagnosing issues related to color vision deficiencies, making it the correct answer.