what is axis on eye prescription

The axis on an eye prescription is a number that indicates the direction in which any cylindrical power in the lenses must be positioned to correct astigmatism. The axis number shows the orientation or angle of the eye in degrees ranging from 1 to 180, with 90 representing a vertical position and 180 representing a horizontal position. The axis value is required when an eyeglass prescription has cylinder power (CYL value), which is the strength of astigmatism correction needed, and it directs where to place the power in the lenses of your glasses. It is important to note that a higher axis number does not mean a stronger prescription, as it only determines the position of the eyes astigmatism.