Astigmatism is a refractive error primarily caused by what?

Astigmatism is primarily caused by an irregular curvature of the cornea or lens. In individuals with astigmatism, the cornea or lens is shaped more like a football rather than a perfect sphere. This irregular shape causes light to be focused at multiple points in the eye or not focused at all, leading to blurred or distorted vision. Correcting astigmatism typically involves the use of glasses, contact lenses, or refractive surgery that aims to reshape the cornea, allowing for better focus of light onto the retina.

The other options do not accurately describe the primary cause of astigmatism. Excessive intraocular pressure is associated with glaucoma, not astigmatism. Blockage in the tear ducts relates to issues with tear drainage and does not affect the refractive properties of the eye. Increased age-related changes can lead to various eye conditions, such as presbyopia or cataracts, but they do not specifically cause astigmatism, which is linked to the structural shape of the cornea or lens rather than age alone.