Name one common cause of astigmatism.

An irregularly shaped cornea is a common cause of astigmatism because it affects how light is refracted onto the retina. In a normally shaped cornea, light rays are bent evenly and focus at a single point on the retina, allowing for clear vision. However, when the cornea has an irregular shape—either steeper in one direction or flatter in another—it causes light rays to focus on multiple points either in front of or behind the retina. This results in blurred or distorted vision at different distances, which encapsulates the essence of astigmatism.

Other options do not directly relate to the primary anatomical cause of astigmatism. Excessive exposure to light influences comfort and may lead to other issues like photophobia, but it does not structurally alter the cornea. High levels of eye strain can exacerbate visual discomfort but are not a direct origin of astigmatism itself. Age-related muscular degeneration primarily affects the macula and vision clarity associated with aging but does not pertain to the corneal shape that leads to astigmatism.