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': 'All the following signs could result from infection within the right cavernous sinus except - \nSelect and explain. \nA. Constricted pupil in response to light, B. Engorgement of the retinal veins upon ophthalmoscopic examination, C. Ptosis of the right eyelid, D. Right Ophthalmoplegia', 'role': 'user'}, {'content': 'Answer: A \nExplanation: In CST, there is loss of direct and consensual light reflex on the same side. So, there will be no pupillary constriction in response to light.\nRetinal veins are engorged and congested in later stages.\nPtosis (due to 3rd nerve involvement) and opthalmoplegia (due to 3rd, 4th, 6th nerve involvement) occur in CST.', 'role': 'assistant'}]