Astigmatism
Astigmatism
In optics, different objects have different "refractive indices." When light enters the eye from the air, its refractive index changes, and its direction of travel also changes; this is known as "refraction." Light emitted or reflected from distant and near objects in the external environment must be refracted by the eye's optical system before it can converge and form an image on the retina. Astigmatism is a refractive error caused by an imperfectly curved surface of the cornea or lens. This prevents the image of an object from forming a single clear focus on the retina when it enters the eye, resulting in blurred vision. Based on the refractive condition, astigmatism can be broadly divided into two types: Irregular astigmatism: Cannot be corrected with cylindrical lenses. Regular astigmatism: Can be corrected with cylindrical lenses or surgery, often resulting in good visual acuity. Astigmatism is very common; everyone has some degree of astigmatism, though some people have a mild degree that they do not notice in daily life. The main symptoms include blurred vision, monocular diplopia (seeing double with one eye), and eye fatigue.
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