Updated: January 14, 2026
OD means your right eye and OS means your left eye, and your contact lens prescription lists separate lens details for each eye so you can order the correct lens power and fit. These two-letter abbreviations show up on almost every prescription, and mixing them up is a common reason people end up with the wrong lenses. Once you know where to look, reading your prescription becomes much less intimidating and a lot faster.
What to Check:
1. OD is the right eye, OS is the left eye, and OU may be used for both eyes.
2. PWR or SPH is the lens power in diopters, with a minus sign for nearsightedness and a plus sign for farsightedness.
3. BC (base curve) and DIA (diameter) are fit measurements that help the lens sit correctly on your eye.
4. If you have astigmatism, look for CYL and AXIS, and if you need multifocals, look for ADD.
5. Use the exact lens brand or manufacturer and check the prescription expiration date, because glasses prescriptions are not the same as contact lens prescriptions.
Reading OD and OS correctly helps you match each eye to the right contact lens power, fit details, and prescribed brand for safe, accurate ordering.
Disclaimer: This information is for general informational purposes only and is not a substitute for professional advice, diagnosis, or treatment.
References:
How to Read an Eyeglasses Prescription. American Academy of Ophthalmology (AAO). https://www.aao.org/eye-health/glasses-contacts/how-to-read-eyeglasses-prescription. Updated April 18, 2023.
Contact Lens Prescription. U.S. Food and Drug Administration (FDA). https://www.fda.gov/medical-devices/contact-lenses/contact-lens-prescription. Content current as of October 28, 2020.
The Contact Lens Rule: A Guide for Prescribers and Sellers. Federal Trade Commission (FTC). https://www.ftc.gov/business-guidance/resources/contact-lens-rule-guide-prescribers-sellers. Published May 28, 2004.
