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': 'Cataract brunescens result due to deposition of: \nSelect and explain. \nA. Melanin, B. Copper, C. Iron, D. Silver', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. Melanin', 'role': 'assistant'}]