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': 'Lesion at which pa of visual pathway causes homonymous hemianopia? \nSelect and explain. \nA. Optic tract, B. Optic nerve, C. Optic Chiasma, D. Retina', 'role': 'user'}, {'content': "Answer: A \nExplanation: A left homonymous hemianopsia can be caused by a lesion in the right optic tract or the right side of the brain. With a tract lesion, the pupillary reflex is lost if light is only projected from the blind hemifield; the pupil reacts when the lesion is posterior to the geniculate body in the optic radiations or occipital lobe. Transient homonymous hemianopsia may occur with migraine. Ref: LeBlond R.F., DeGowin R.L., Brown D.D. (2009). Chapter 7. The Head and Neck. In R.F. LeBlond, R.L. DeGowin, D.D. Brown (Eds), DeGowin's Diagnostic Examination, 9e.", 'role': 'assistant'}]