OD and OS are abbreviations used in eyeglass prescriptions to indicate the left and right eyes, respectively. OD stands for "oculus dexter," which is Latin for "right eye," while OS stands for "oculus sinister," which is Latin for "left eye". Sometimes, doctors may use "RE" or "right" instead of OD, and "LE" or "left" instead of OS. If both eyes require the same prescription, the abbreviation OU, which stands for "oculus uterque," meaning "both eyes" in Latin, may be used. The numbers listed next to OD and OS indicate the strength of the correction necessary to focus light properly inside the eye.