During subjective refraction of a 20-year-old myope, the duochrome (red-green) test is performed. The patient reports that the letters on the green side appear sharper than those on the red side. The correct action is:

• A Add more minus power
• B Reduce the minus power ✓
• C Add plus power
• D The result indicates accurate end point

Explanation

Chromatic aberration focuses shorter (green) wavelengths slightly in front of longer (red) wavelengths. If the eye is over-minused, its focal point is pulled forward, so green letters come into focus on the retina first and appear clearer. The correction is to reduce minus (or add plus) until red and green appear equally clear, the balanced end point. Adding further minus would worsen the overcorrection and push accommodation, so option A reverses the true finding.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.