An astigmatism occurs when the cornea is shaped more like a football than a perfect sphere causing a refractive error in which light rays entering the eye do not focus onto a single point needed for clear vision. Instead, light focuses on two distinct points, neither of which may be on the retina. Where these images focus depends on whether the astigmatism is associated with myopia, or hyperopia. Astigmatism causes a distortion or blurring of images at all distances.

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