To understand your contact lens prescription, it helps to know that your right eye is always listed first, and is usually marked “OD” for oculus dexter; the left eye comes next, and is marked “OS” for oculus sinister. There’s no physical difference between a right and left contact lens — OD and OS simply tell you which eye needs which lens power.
The lens power (PWR) or sphere (SPH) is the amount of vision correction each eye needs to achieve 20/20 vision. Make sure you take note of the sign in front of your power: a plus sign (+) means that you have farsightedness, while a minus sign (-) indicates nearsightedness.
If you have astigmatism (distortion and blurring caused by an irregularly shaped cornea), your prescription will also include values for cylinder (CYL) and axis (AXIS). If you have astigmatism in only one eye, you'll enter a CYL and AXIS of "0/None/DS" for the eye without astigmatism.
For more information about your prescription and what it can tell you about your eyes, check out our blog article!