How to read an eyeglass prescription

If you often wonder how to order prescription glasses online, knowing how to read your eyeglass prescription is the first crucial step. In the US, you always have the right to get a written copy of your glasses prescription after your eye exam. This guide, updated for 2025, explains every prescription value and helps you shop confidently on Glasses.com.

What Is an Eyeglass Prescription?

Every valid prescription in the US includes all information required to purchase eyeglasses online or in-store, and to use your vision insurance benefits.

Glasses Prescription Chart: Key Terms Explained

S (Sphere) – Nearsighted vs Farsighted

The “sphere” (SPH or S) helps correct nearsightedness (with a “-” value) or farsightedness (with a “+”). The farther from zero, the stronger the lens.
→ Shop prescription glasses with Sphere correction

CYL (Cylinder) & Axis – Astigmatism Explained

For astigmatism, prescriptions show “cylinder” (CYL) as a + or – and the “axis” (0–180°). This combo brings vision into sharper focus for those with an irregular cornea shape.
→ Details about astigmatism

OS, OD & OU – Which Eye?

OD = right eye, OS = left, OU = both eyes. These Latin abbreviations always point to which measurements refer to which eye.
→ Glossary: Prescription abbreviations

PD (Pupillary Distance) – Why it Matters

PD (pupillary distance) is the measurement in millimeters between your pupils. It’s essential for perfectly centered lenses.
Measure your PD at home with our printable ruler or read our PD measurement guide.

Prism – What Does it Correct?

Prism correction is sometimes added to treat double vision or eye misalignment, noted as BI/BO/BU/BD.
→ More on prism correction and symptoms

How to Interpret Your Prescription Chart (with Example)

Don’t see your PD? Use our online tool and guide.

How Can I Get My Eyeglass Prescription in the US?

By US law (FTC’s Eyeglass Rule), your doctor must provide your glasses prescription after each full eye exam. Read more on how often you should get an eye exam and how to use your insurance. For exam locations, find eye doctors near you through our provider locator.

FAQ on Eyeglass Prescriptions (US-specific)

• How long is a glasses prescription valid in the US?
• Can I order glasses online with any prescription?
• What if my PD is missing?
• What does “Add” mean?
• What’s the difference between eye exam and vision screening?

Next Steps: Order Your Prescription Glasses Online

Now you’re ready to shop your prescription glasses on Glasses.com. For step-by-step guidance, follow our complete guide to ordering glasses online. If you need more support, contact our team or check the FAQ section.