Which error of refraction occurs due to an abnormally shaped eyeball?

The question pertains to errors of refraction, specifically asking which type arises from an abnormally shaped eyeball. The correct answer is astigmatism, which often results from the cornea or lens being irregularly shaped.

Astigmatism occurs when the curvature of the cornea or lens deviates from the normal spherical shape, leading to multiple focal points instead of a single point of focus. This results in blurred or distorted vision at all distances. When the cornea is more steeply curved in one direction than the other, it causes the light rays entering the eye to refract unevenly, manifesting as astigmatism.

The other choices focus on different types of ocular issues. Myopia, or nearsightedness, generally stems from the eye being too long from front to back, causing light rays to focus in front of the retina. Presbyopia is an age-related condition where the eye's lens loses its flexibility, primarily affecting the ability to focus on close objects. The term "errors of refraction" is a broad classification that encompasses various refractive disorders, but it does not specifically identify a particular condition related to the shape of the eyeball.

Thus, the correct understanding lies in recognizing that astigmatism