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': 'What will be the prescription for spectacles in a patient having simple myopic with the rule astigmatism? \nSelect and explain. \nA. -0.5D at 180 degrees, B. +0.5D at 180 degrees, C. -3.0D at 90 degrees, D. +2.0D at 90 degrees', 'role': 'user'}, {'content': 'Answer: A \nExplanation: -0.5D at 180 degrees With the rule astigmatism - two principal meridian are at right angles with the veical meridian being more curved. Correction requires convex(+) cylinder at 90 degrees or concave (-) cylinder at 180 degrees. Myopic astigmatism means the patient has to be given a concave cylindrical lens. Against the rule astigmatism corrected by = convex(+) C at 180 degrees or concave (-) C at 90 degrees Option 4 +2.0D at 90 degrees is also with the rule astigmatism but this patient will have simple hyperopic with the rule astigmatism not simple myopic as expected from the question', 'role': 'assistant'}]