Axis is a specialized term that most often used in describing the orientation of Astigmatism in degrees in eye prescription form. That is to say, the axis is the measurement required for the contact lens to correct the astigmatism. The measurements on the prescription will be preceded by either a positive (+) or a negative (-) sign.
The character of "Axis" means the radius of curvature of the lenses. The greater the arc, the flatter the inner surface of the lens. If lenses base arc is bigger than eyeball base arc, it may appear that lenses are not sticked to the eyes which may be easily fallen out. If lenses base arc is less than eyeball base arc, it's easy to let an eye have tight uncomfortable feeling. Of course,it is better to be consistent. In the ordinary circumstances, lens base arc and eyeball base arc difference should be controlled in less than 0.2 mm.