Corrective Lenses can either be spherical or cylindrical. The purpose of an eyeglass is to alter the focal length and point of focus in the eye. The focusing ability of an eyeglass is determined by the difference in curvature on its front and back surface, its thickness and its index of refraction. The precise lens can then be chosen to correct any vision condition.

Spherical Lenses

Cylindrical lenses are used most often to correct astigmatism.

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