This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Optics and Errors of Refraction, Subject name: Ophthalmology
[{'content': 'Pin hole test is used for: \nSelect and explain. \nA. Keratoconus, B. Refractive error, C. Presbyopia, D. only Astigmatism', 'role': 'user'}, {'content': 'Answer: B \nExplanation: PIN HOLE TEST - Completely opaque plastic device with central hole (1mm diameter) - It allows single ray of light that passes through nodal point of eye. - On applying this if vision improves = optical error ( Myopia , Hypermetropia, Astigmatism) if vision do not improves= organic error (macular disease, dense cataract, retinal detachment, retinal diseases) It does not differentiates type of optical error', 'role': 'assistant'}]