How does a rigid lens correct astigmatism?

Astigmatism is a refractive error caused by an irregular shape of the cornea or lens, leading to blurred vision at different angles. Rigid gas permeable (RGP) contact lenses can effectively correct this condition by creating a new cylindrical refracting surface on the eye. When the RGP lens is placed on the cornea, it mimics the shape of the cornea and creates a new optical surface that compensates for the existing astigmatism.

This is achieved because the RGP lens maintains its shape and doesn't conform to the irregularities of the cornea, unlike soft lenses. As light passes through the RGP lens, it is properly refracted, which allows for clearer vision. The lens essentially reshapes the way light enters the eye, providing a cylindrical correction that aligns with the axis of astigmatism.

Creating a new spherical refracting surface would not address the irregular curvature of the eye necessary for astigmatism correction. Changing the lens shape and increasing the lens diameter do not directly create the necessary optical changes needed to correct astigmatism either. The focus is on how the lens interacts with the eye's surface to modify the light entering the eye, which is key to treating astigmatism