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': 'Commonest cause of uniocular diplopia \nSelect and explain. \nA. Cataract, B. Subluxated lens, C. Third nerve palsy, D. Astigmatism', 'role': 'user'}, {'content': 'Answer: B \nExplanation: In Unilocular diplopia an object appears double from the affected eye even when the normal eye is closed. CAUSES Subluxated clear lens. Subluxated intraocular lens. Keratoconus (irregular refraction from corneal surface) Double pupil (congenital / large iridectomy / iridodialysis) Incipient cataract (this usually causes polyopia - due to irregular refraction due to multiple water clefts within the lens) Ref;A.K.Khurana; 6th edition; Page no:344', 'role': 'assistant'}]