Astigmatism

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Astigmatism is a vision problem that occurs when the lens or cornea of an eye are slightly egg-shaped rather than spherical. The lack of rotational symmetry causes a refractive error that cannot be corrected with simple glasses. The astigmatism causes distorted or blurred vision at any distance and requires corrective lenses that apply different optical powers at different rotational angles. Astigmatism can lead to symptoms that include eyestrain, headaches, and trouble driving at night. Often it is present at birth, but it can change or develop later in life, and so can affect people of all ages. If it occurs in early life and is left untreated, it may result in amblyopia. The cause of astigmatism is unclear, although it is believed to be partly genetic. The underlying mechanism involves an irregular curvature of the cornea and protective reaction changes in the lens of the eye, called lens astigmatism, that has the same mechanism as spasm of accommodation. Diagnosis is both objective...

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