Which refractive error involves the eye's inability to focus at various distances?

Astigmatism is a refractive error that occurs due to an irregular shape of the cornea or lens, which prevents light from focusing properly on the retina. This irregularity results in distorted or blurred vision at various distances. Individuals with astigmatism often experience difficulty seeing clearly, whether looking at objects up close or far away, because the light entering the eye does not converge to a single focus point.

When the eye’s surface or lens has an uneven curvature, light rays may be focused at different points, leading to a consistent struggle to achieve clear vision, regardless of distance. This is what distinguishes astigmatism from other types of refractive errors, such as myopia (nearsightedness) and hyperopia (farsightedness), which primarily affect vision at specific distances rather than causing an overall inability to focus across various ranges. Amblyopia, on the other hand, is not a refractive error but a developmental issue leading to decreased vision in one eye, often requiring different approaches for correction.