The Ishihara chart primarily screens for which type of color vision deficiency?

• A. Red-green color deficiency
• B. Blue-yellow color deficiency
• C. Total color blindness
• D. Diamond color deficiency

Answer: (C)

The Ishihara chart is designed to detect red-green color vision deficiencies. It uses plates with colored dot patterns that form numbers or shapes visible to people with normal red-green vision but appear different or indistinguishable to those with red-green deficiencies. This type of deficiency, due to issues with the long- and medium-wavelength cones, is by far the most common inherited color problem, which is why the chart focuses on it. Blue-yellow deficiencies involve different cone types and are not reliably screened by these plates, and total color blindness (achromatopsia) would affect color perception more broadly and isn’t the target of this test.