Understanding Your Prescription

Common refractive disorders of the eye such as myopia, hyperopia, astigmatism, and presbyopia are measured in units called diopters. Diopters represent the amount of correction you need to normalize your vision. The more nearsighted, farsighted, or astigmatic you are, the higher your prescription in diopters.

An example of a prescription is:

The term OD (oculus dextrum) stands for "Right eye" and OS (oculus sinistrum) for the "Left eye".

The "Sphere" column indicates how nearsighted or farsighted you are. A plus (+) power indicates farsightedness and a minus (-) power indicates nearsightedness.

"Cylinder" refers to the measurable degree of astigmatism of your central cornea.

If you have astigmatism, your cornea is shaped like the back of a spoon, curved more on one side than the other. The orientation of the spoon shape can differ from person to person. The "Axis" column describes the orientation in degrees from the horizontal. The coordinate system for the prescription is 0 to 180 degrees with 90 at the vertical or 12 o'clock position.