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What is astigmatism in the eyes?

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Astigmatism is a condition that causes blurred vision when the lens or cornea of an eye has an irregular surface contour, according to Mayo Clinic. Rather than having a consistently smooth curvature, an astigmatic lens or cornea has abnormal curves and flattened areas, changing how the eye processes light.

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As light passes into the eye, the cornea and lens work together to focus incoming rays toward the retina and produce a clear image, explains the American Optometric Association. Shape irregularities can change how different sections of the cornea or lens surface refract light, distorting the eye's focal point. For example, the corneal surface may be oval-shaped instead of spherical. If the condition is not present at birth, it may develop after a surgery or injury.

Astigmatism is known as a refractive error, and physicians usually classify it as corneal or lenticular, notes Mayo Clinic. Blurriness caused by refractive distortion occurs in the same direction as the abnormal curvature, such as vertically, horizontally or diagonally. In addition to vision problems, people with astigmatism may develop headaches or eye strain.

Serious cases are often accompanied by myopia, known as nearsightedness, or hyperopia, known as farsightedness, according to Mayo Clinic. In a nearsighted eye, an excessively curved cornea shortens the point of focus, making far off objects seem blurry. In farsighted vision, a cornea lacking curvature or an unusually short eye makes the point of focus longer than normal, so closer objects appear blurry.

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