This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Ophthalmology
[{'content': 'Relative afferent pupillary defect  is characteristically seen In damage to \nSelect and explain. \nA. Optic nerve, B. Optic tract, C. Lateral geniculate body, D. Occulomotor nerve', 'role': 'user'}, {'content': 'Answer: A \nExplanation: For testing relative afferent pupillary defect (RAPD), a strong, steady light is used. \nThe light is shined into one eye, and then quickly switched to the other. \nThis is repeated back and forth, until one of four conclusions is reached (listed below).\nSince light in one pupil causes both pupils to constrict, quickly switching from one eye to the other will give a "relative" indication of the functioning of each eye and optic nerve.\nIf both eyes are equally dysfunctional, no "relative" defect would be found.', 'role': 'assistant'}]