While performing duochrome test, If the patient repos that he sees red letters more clear than green, it indicates that he is slightly
Duochrome test: It is based on the principle of chromatic aberration. In this, the patient is asked to read the red and green letters. In an emmetropic eye the green rays are focused slightly anterior and red rays slightly posterior to the retina. Therefore, to an emmetropic patient letters of both colours look equally sharp. When the patient tells that he or she sees red letters more clearly than the green, it indicates that he or she is slightly myopic. Technique One eye is occluded Subject is asked to note whether the letters on the cha are equally visible or prominent on both backgrounds or more visible or prominent against one of the backgrounds Vision is slightly fogged by adding plus(+) sphere monocularly in 0.25DS steps until red background letters become more prominent This should occur in only one / two increments of plus power unless the eye has been over corrected The plus powered sphere before the eye is reduced until both background letters appear equally distinct. This represents optimum correction Next reduction causes green to be more prominent Reference :- A K KHURANA; page:-556
Myopic
Hypermetropic
Presbyopic
Emmetropic
Optics and refraction