Concept:Astigmatism is a refractive error caused by an uneven curvature of the cornea or the lens.
Explanation:In a normal eye, the cornea and lens have a smooth, evenly curved surface, like part of a sphere.
This uniform shape helps focus light rays directly on the retina.
In astigmatism, the cornea or lens is more curved in one direction than in another.
Because of this uneven curvature, light cannot focus evenly on the retina.
This causes blurred or distorted vision at both near and far distances.
Myopia affects distant vision, hypermetropia affects near vision, and presbyopia is age-related loss of near vision.
Only astigmatism is specifically caused by the irregular shape of the cornea or lens.
Answer:C. astigmatism