Ever wonder what the letters and numbers meant on your lens prescription? Here’s a quick help guide. OD is your right eye is short for oculus dexter, OS is your left eye short for oculus sinister, and If you see OU that is both eyes and short for oculus uterque. And now for numbers, typically the further away from zero you have on your prescription, the worse your vision correction is needed. Now when you see a (-) minus it means you are nearsighted and (+) plus means you are farsighted.