It also indicates if the patient has astigmatism. So if your prescription reads o.d. The measurement used in eye prescriptions is the diopter. The sphere measure tells the eye doctor whether light focuses on the retina, in front of the retina or behind the retina. Negative diopters indicate myopia, or nearsightedness.
Positive diopters indicate hyperopia, or farsightedness.
The higher the number, the stronger the prescription. The cylinder measurement indicates whether or not the patient has astigmatism. If any number appears in the cylinder column, then some astigmatism is present. The higher the number, the more severe the astigmatism. If astigmatism is present, then an axis measurement is also necessary.