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What is Prescription of simple myopic astigmatism: and explain in detail?
Ans. a.-0.5x180degSimple myopic astigmatism is one in which one meridian is emmetropic and other meridian is myopic.Hence needs correction only in one meridian with concave (-ve) cylinders. So the answer is -0.5x180deg.ASTIGMATISM TYPES AND CORRECTIONTypes of astigmatismDescriptionOpticsCorrectionSimple myopic astigmatismOne of the foci falls upon the retina while the other falls in front of or behind the retinaConcave cylinder Ex: -0.5x180degConvex cylinder Ex: +0.5x180degSimple hyperopic astigmatismCompound myopic astigmatismNeither of the foci fall upon the retina but both are placed infront of or behind the retinaConcave sphere + Cylinder Ex: -0.5 D sphere, -0.5x180degConvex sphere + Cylinder Ex: +0.5 D sphere, +0.5x180degCompound hyperopic astigmatismMixed astigmatismOne focus is front of the retina while the other is behind so that the refraction is hypermetropic in one direction and myopic in other directionConcave/ConvexSphere+Convex and concavecylinderEx: -1D sphere, +2Dx180deg