Medicine and law have roots in ancient Rome and use many Latin terms and abbreviations. In ophthalmology, the branch of medicine treating the eye, O.D. and O.S. are commonly used abbreviations referring to the right and left eye.
An eye exam measures vision, evaluating how well a patient can see, both far and near, as well as color and depth perception. During an eye exam, an ophthalmologist or optometrist looks for signs of eye disease and disorders like glaucoma or cataracts. Your doctor assesses each eye separately writes prescriptions for right and left eye.
When writing eye exam results on a chart or for a prescription, an eye doctor uses the abbreviations for the Latin terms meaning right and left eye. O.D. stands for oculus dexter, or right eye; it means pertaining to the right eye. O.S. means oculus sinister, or left eye. Eye doctors sometimes use the abbreviation O.U, which means both eyes.
Reading a Prescription
The terms O.D. and O.S. categorize a prescription for eyeglasses, contacts or therapy. For example, on an eyeglass prescription, numbers under each heading indicate the vision correction needed. The further from zero the number is, the stronger the prescription for either the right or left eye. A negative sign indicates that the correction is for nearsightedness; a plus sign means that the correction is for farsightedness.
The Latin word meaning left is sinestra, which medical or technical documents sometimes used instead of left handed. At times, left-handedness has had negative connotations, which explains its connection to the word sinister. The Latin word for right-handed is dexter, which is the root of the word dexterity and related to skillful.
In 2004, the Joint Commission on Accreditation of Healthcare Organizations (JCAHO) suggested that the abbreviations O.D., O.S. and O.U. create confusion and could be mistaken for one another. JCAHO recommended that "right eye," "left eye" and "both eyes" be written in full.