What is a refractive error where light rays do not focus at a single point?

Astigmatism is characterized by an irregular curvature of the cornea or lens, which causes light rays to be focused at multiple points, rather than a single point on the retina. This results in blurred or distorted vision, as the eye's ability to focus is compromised. Unlike myopia (nearsightedness) and hyperopia (farsightedness), which are primarily related to the overall length of the eyeball and the refractive power of the eye's lenses, astigmatism specifically relates to its uneven surface. The condition can occur in combination with myopia or hyperopia, which adds to its complexity. Understanding that astigmatism is marked by light focusing at several points rather than one emphasizes its unique distinction from other refractive errors.