This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cataract, Subject name: Ophthalmology
[{'content': 'Christmas tree appearance seen in: \nSelect and explain. \nA. Myotonic dystrophy, B. Trauma, C. Chalcosis, D. Diabetes', 'role': 'user'}, {'content': 'Answer: A \nExplanation: About 90% of patients with myotonic dystrophy develop fine iridescent coical opacities in the third decade, sometimes resembling Christmas tree cataract.', 'role': 'assistant'}]