what is cylinder on eye prescription

A cylinder on an eye prescription refers to the amount of lens power needed to correct astigmatism. It always follows the sphere power on the prescription and is measured in diopters. The cylinder indicates the difference in the greatest and weakest powers of the eye, usually separated by 90 degrees. If the cylinder column is empty, it means that either you have no astigmatism, or your astigmatism is so slight that it does not need to be corrected with your eyeglass lenses