This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Optics and refraction, Subject name: Ophthalmology
[{'content': 'Duochrome test is for - \nSelect and explain. \nA. Subjective verification of refraction, B. Subjective refinement of refraction, C. Subjective binocular balancing, D. Subjective monocular balancing', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Duochrome test is based on the principle of chromatic aberrations. It helps in verifying the spherical correction subjectively. In it, the patient is asked to tell the clarity of the letters with red background visa- vis green background. To an emmetropic patient letters of both the colours look equally sharp; while to a slightly myopic patient the red letters appear sharper and to a slightly hypermetropic patient the green letters look sharper. Reference : A K KHURANA OPHTALMOLOGY,Edition 4, Page-563', 'role': 'assistant'}]