What type of lens is primarily used for correcting astigmatism?

Cylindrical lenses are specifically designed to correct astigmatism, which is a refractive error caused by an irregular shape of the cornea or lens of the eye. In a normal eye, light rays focus on a single point on the retina, but in the case of astigmatism, light rays are focused on multiple points, leading to distorted or blurred vision at various distances.

Cylindrical lenses have different curvatures in different meridians, allowing them to bend light more in one direction than the other. This characteristic enables them to compensate for the uneven curvature of the cornea or lens, thus providing clear vision by properly aligning the light rays onto the retina. The orientation of the cylindrical power is defined by the "axis," which specifies the meridian that needs correction.

Other types of lenses, such as spherical or aspherical, do not have the necessary properties to address the specific focusing issues associated with astigmatism. Progressive lenses are multifocal lenses designed for presbyopia and do not specifically target astigmatism correction in the same way that cylindrical lenses do. Therefore, using a cylindrical lens is essential for effectively managing and correcting astigmatism.