The numbers and abbreviations you see in your prescription relate to the shape of your eye and strength of vision. The abbreviation OD (oculus dexter) refers to your right eye, OS (ocular sinister) your left eye, and OU (oculus uterque), means both eyes. Some doctors have however abandoned these Latin terms or abbreviations and instead write RE (right eye) or LE (left eye). Generally, if the number on your prescription is further away from zero, it means you require a stronger prescription. Lens power is measured in diopters (D), which help to establish the necessary focusing power. For example, if the reading on your left eye is -4.25, you have 4.25 diopters of nearsightedness and require stronger lenses. A reading of -1.00, on the other hand, represents one diopter of nearsightedness. The sphere box will have either a minus (-) symbol next to the number (the lens power needed to see clearly) to correct nearsightedness or a plus (+) symbol if you are farsighted. If your prescription contains CYL (cylinder), it means you have astigmatism, and that is the lens power required to correct it. Some do not have CYL. Those with astigmatism will also have an axis number, which indicates the lens' angle that should not feature a cylinder power to correct astigmatism. Three numbers of prescriptions represent astigmatism, that is, S (spherical) x C (cylinder- either negative or positive) x Axis (any number between 0 and 180). Other terms you need to be aware of include base and prism. The base and prism are used to correct eye alignment problems since they indicate how to shape the lens to be accurately aligned to the wearer's eyesight. The prism's direction should be angled by the base value that shows either 'in' or 'out' or 'up' or down.'