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
Which enzyme is defective in Refsums disease? 
Select and explain. 
A. Phytanic acid oxidase, B. Succinate thiokinase, C. Malonate dehydrogenase, D. Thiophorase
A: Phytanic acid oxidase
Answer: A: Phytanic acid oxidase 
Explanation: A. i.e. Phytanic acid oxidase