Not all eyeglass prescriptions are the same. In order to be interpreted worldwide, eyeglass prescriptions are writtenin a standardized format with common notations. Notable terms include:
Sphere (Sph) : Sphere sph is the measurement of how much your eye needs to be corrected to see clearly. Sphere (Sph) is often referred to as “power” or “minus cylinder.” If the number appearing under this heading has a minus sign (–), you are nearsighted; if the number has a plus sign (+) or is not preceded by a plus sign or a minus sign, you are farsighted.
Cylinder (Cyl) : Cylinder cyl is the power of one live eye corrected for astigmatism. It represents the difference in greatest and weakest powers. If you have astigmatism, the cylinder power will be listed right next to your sphere power. If nothing appears in this column, either you have no astigmatism, or your astigmatism is so slight that it is not necessary to correct it with your eyeglass lenses. The number in the cylinder column may be preceded with a minus sign (for the correction of nearsighted astigmatism) or a plus sign (for farsighted astigmatism). Cylinder power always follows sphere power in an eyeglass prescription.
Axis (Ax) : If an eyeglass prescription includes cylinder power, Ax Axis also must include an axis value, which defines the angle (in degrees) between the two meridians of an astigmatic eye. The axis is defined with a number from 1 to 180. The number 90 corresponds to the vertical meridian of the eye and 180 corresponds to the horizontal meridian.