What is axis in eye prescription?

The axis is a number between 1 and 180 that indicates the orientation of astigmatism in an eye prescription. It is measured in degrees and represents the angle at which the cylindrical power (also known as the astigmatism correction) should be placed on a corrective lens in order to correct the irregular curvature of the cornea and lens of the eye. The axis helps to ensure that the cylindrical power is aligned correctly with the astigmatism in the eye, allowing for improved vision clarity and focus.