Can the duochrome test be used in patients with red-green color deficiencies?

• A. Yes
• B. No
• C. Only if color vision is corrected
• D. Not recommended

Answer: (A)

The duochrome test works because of the eye’s chromatic aberration, not color naming. Red and green light focus at different distances due to longitudinal chromatic dispersion, so when the refraction is correct, letters on both red and green sides should look equally sharp. A color-deficient patient doesn’t need to distinguish the colors themselves; they only judge which side’s letters appear crisper. Since the test hinges on sharpness rather than color recognition, red-green color deficiencies do not prevent using the test.