How to Read Your Vision Prescription

Submitted by GemStateEyes on Mon, 06/27/2022 - 11:24
hand holding a white form with glasses prescription

When you receive your eyeglasses or contact lenses prescription, you might be wondering what the various codes and abbreviations mean. In this blog, we will walk you through the definitions and everything you need to know about your vision prescription.

OS and OD

OS is an abbreviation for the Latin term oculus sinister, which means “left eye”. OD is the abbreviation for oculus dextrus, which means “right eye”. You might also see OU, which is short for oculus uterque, meaning “both eyes”. You will see these abbreviations on both eyeglasses and contact lens prescriptions. Some doctors may modernize their prescriptions by using LE for the left eye and RE for the right eye.

(BC) Base Curve

For contact lenses, the base curve is the measurement that is required for the lens to fit the curve of your eye. This number is usually between 8 and 10.

(SPH) Sphere

The Sphere number indicates the lens power that is needed to correct farsightedness or nearsightedness. Your lens power is measured in diopters (D).

  • If you are farsighted, the number will have a plus sign in front of it (+).
  • If you are nearsighted, the number will have a negative sign in front of it. (-).

This entry on your prescription might have PWR instead of SPH, which means Power.

(CYL) Cylinder

The Cylinder number indicates the lens power that is needed to correct astigmatism. This is also measured in diopters. On an eyeglasses prescription, you’ll see this listed next to the Sphere number. The Cylinder may have a minus sign for nearsighted astigmatism or a positive sign for farsighted astigmatism.

(AX) Axis

Astigmatism happens when you have an irregular curvature of the eye. Therefore, the Axis number indicates the angle of the correction needed for clear vision. This number will be between 0 and 180 degrees.

(DIA) Diameter

For contact lenses, the Diameter number indicates the width that best fits your eye. This is usually a number between 13 and 15.

(ADD) Addition

Addition is the added magnifying power used to correct presbyopia, which is a change in focus that occurs with age. This number will always be a plus power, and the range is usually from +0.75 to +3.00 D.


This number is the amount of prismatic power, which corrects eye alignment issues. You’ll see this measured in prism diopters (p.d.). The Prism is measured in metric or fractional units, such as .5 or ½.

The prism directions have 4 abbreviations:

  • BU: Base Up
  • BD: Base Down
  • BI: Base In (inward towards the nose)
  • BO: Base Out (outward toward the ear)

Other Details on Your Prescriptions

As you may have noticed, your contact lenses prescription will be slightly different from the eyeglasses prescription. Your eye doctor will issue them separately after your eye exam, and it’s important to keep them on file when refilling your contact lenses and selecting your new eyeglasses.

On your prescription for contact lenses, you may see more information such as the brand your doctor recommended and used for the fitting and how often you should dispose of the contacts (monthly, bi-weekly, weekly, daily). In some cases, if you have astigmatism or bifocal in one eye, your doctor may use two separate brands for each eye.

On your prescription for glasses, your doctor may write more suggestions such as anti-reflective coating, photochromic lenses, or progressive lenses to accommodate any other eye issues.

Schedule Your Eye Exam

If you need help with understanding your prescriptions, we are happy to help! Contact us for any questions, or schedule your next eye exam today.