OS (lens prescription): Abbreviation of "oculus sinister." Latin for "left eye." By contrast, OD stands for "oculus dexter" which is Latin for the right eye. SLIDESHOW Pink Eye (Conjunctivitis) Symptoms, Causes, Treatments See Slideshow From Eye Health Resources Eye Care When You Have Graves' Eye DiseaseFinding the Care You Need for MS Featured Centers Good and Bad Foods for PsoriasisVideo: Getting Personal on Life With MS Health Solutions From Our Sponsors Shot-Free MS Treatment Your Child and COVID-19