Astigmatism primarily affects which part of the eye?

Astigmatism is primarily associated with an irregular curvature of the cornea, the clear front surface of the eye. In a healthy eye, the cornea has a uniform curvature that helps focus light evenly onto the retina. However, in astigmatism, the cornea is shaped more like a football—curved more in one direction than the other. This irregular shape prevents light from focusing properly, leading to blurred or distorted vision.

While the lens, iris, and retina play significant roles in vision as well, they are not the primary structures affected in astigmatism. The lens focuses light onto the retina but does not typically contribute to the astigmatic condition itself. The iris controls the amount of light entering the eye, and the retina is responsible for converting light signals into neural signals for the brain, but both remain unaffected by the condition of astigmatism. Thus, the correct answer highlighting the part of the eye primarily involved in this refractive error is the cornea.