Final answer:
Astigmatism occurs when there is significant asymmetry of the cornea and/or lens. This causes unevenness in the focus of the eye, resulting in less distinct vision or sharper images along certain axes. Eyeglasses with a cylindrical correction can partially correct astigmatism.
Step-by-step explanation:
Astigmatism occurs when there is significant asymmetry of the cornea and/or lens. This unevenness or asymmetry in the focus of the eye can result in an image appearing elongated. The irregularities in the shape of the cornea or lens cause different parts of the lens system to produce images at different locations, leading to less distinct vision or sharper images along certain axes. Astigmatism can be partially corrected with eyeglasses that have a cylindrical correction, which compensates for the irregularities in the eye.