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
Christmas tree appearance seen in: 
Select and explain. 
A. Myotonic dystrophy, B. Trauma, C. Chalcosis, D. Diabetes
A: Myotonic dystrophy
Answer: A: Myotonic dystrophy 
Explanation: About 90% of patients with myotonic dystrophy develop fine iridescent coical opacities in the third decade, sometimes resembling Christmas tree cataract.