This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Lens, Subject name: Ophthalmology
[{'content': 'Cataract brunescen results due to deposition of- \nSelect and explain. \nA. Urochrome, B. Copper, C. Iron, D. Silver', 'role': 'user'}, {'content': 'Answer: A \nExplanation: "Nuclear sclerosis also distos color vision because of-yellow-brown urochrome pigment, chich accumulates in the lens and filters blue wavelenths of light". Older nuclear cells lose organelles and cell membranes, with increasing density and dehydration dnd accumulation of yellow urochrome pigment (possible photo-oxidation product). When advanced, it becomes brown (brunescent) or black (cataracta nigra). Ref: Eye pathology : An Atlas and text p.110.', 'role': 'assistant'}]