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': 'Which enzyme is defective in Refsums disease? \nSelect and explain. \nA. Phytanic acid oxidase, B. Succinate thiokinase, C. Malonate dehydrogenase, D. Thiophorase', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A. i.e. Phytanic acid oxidase', 'role': 'assistant'}]