Guide to Reading Your Eyeglass Prescription
posted: Sep. 23, 2025.
If you’ve ever left the eye doctor’s office with a slip of paper filled with numbers and abbreviations, you may have wondered what your eyeglass prescription really means. At Butler Eye Care in Lebanon, MO, we believe that understanding your prescription helps you feel more confident in your eye care journey. Here’s a simple guide to decoding those numbers.
OD and OS
Your prescription will list OD (oculus dexter) for your right eye and OS (oculus sinister) for your left eye. Sometimes you’ll also see OU, which refers to both eyes. These terms are simply the standard way eye doctors note which eye each measurement applies to.
Sphere (SPH)
The sphere number shows whether you are nearsighted or farsighted. A minus sign (–) before the number means you are nearsighted and see better up close. A plus sign (+) indicates farsightedness, where distant vision is clearer than near vision.
Cylinder (CYL) and Axis
These two numbers address astigmatism, a condition caused by an irregularly shaped cornea or lens. The cylinder tells you the degree of astigmatism correction needed, while the axis indicates the exact orientation of the irregular curve.
Add
If you need bifocals or progressive lenses, you’ll see an Add number on your prescription. This is an extra magnifying power added to help with reading and other close-up tasks, often used for patients over 40 experiencing presbyopia.
Prism
Less common, the prism measurement is used to correct alignment issues in the eyes. This helps reduce double vision or eye strain for patients with specific visual needs.
Making Sense of It All
Your eyeglass prescription may look complicated at first glance, but every number plays an important role in giving you clear, comfortable vision. At Butler Eye Care, our team is here to walk you through your results and answer any questions you may have.
Call Our Optometrist near You to Schedule A Visit Today
If you’re due for an eye exam or need new glasses, schedule a visit with Butler Eye Care in Lebanon, MO, by calling (417) 991-3200. We’ll ensure you not only get the right prescription but also understand it.