This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Retina, Subject name: Ophthalmology
[{'content': 'Anomaloscope is used to detect: \nSelect and explain. \nA. Squint, B. Retinopathy, C. Congenital glaucoma, D. Colour blindness', 'role': 'user'}, {'content': "Answer: D \nExplanation: Nagel's anomaloscope. In this test, the observer is asked to mix red and green colour in such a propoion that the mixture should match the given yellow coloured disc. The judgement about the defect is made from the relative amount of red and green colours and the brightness setting used by the observer. Utility-Colour quantification", 'role': 'assistant'}]