You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Duochrome test is for - and explain in detail?
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