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Knowing how to read your eyeglass prescription is essential to order glasses online or in-store accurately. This guide explains each element of a prescription—SPH, CYL, Axis, PD, and Prism—so you can confidently understand your vision needs and choose the right lenses.
What Is an Eyeglass Prescription?
An eyeglass prescription shows exactly what your eyes need to see clearly. In the US, every prescription includes all the details to buy lenses online, in-store, or with vision insurance. Understanding each part ensures your glasses are correct and comfortable.
Eyeglass Prescription Chart: Key Terms Explained
SPH (Sphere) – Nearsighted vs Farsighted
- SPH or S corrects nearsightedness (-) or farsightedness (+)
- The higher the number, the stronger the correction
CYL (Cylinder) & Axis – Astigmatism Explained
- CYL = lens power for astigmatism (+ or –)
- Axis = 0–180°, shows the orientation of correction
- Helps sharpen vision for irregular cornea shapes
OS, OD & OU – Which Eye?
- OD = right eye, OS = left eye, OU = both eyes
- Latin abbreviations show which eye the measurement applies to
PD (Pupillary Distance) – Why It Matters
- Distance in millimeters between pupils
- Ensures lenses are centered perfectly in your glasses
Prism – What Does it Correct?
- Prism correction helps with double vision or eye alignment issues
- Noted as BI/BO/BU/BD on the prescription
How to Interpret Your Prescription Chart (Example)
| Eye | SPH | CYL | Axis | Add | PD | Prism |
|---|---|---|---|---|---|---|
| OD | -2.00 | -1.25 | 90 | +2.0 | 62mm | BI |
| OS | -1.50 | -1.00 | 85 | +2.0 | – | – |
Steps to follow:
- Verify each number matches your doctor’s prescription
- Ensure PD is accurate for lens centering
- Check for additional corrections like Prism
How Can I Get My Eyeglass Prescription in the US?
- US law (FTC Eyeglass Rule) requires doctors to give a written prescription after every eye exam
- Schedule exams every 1–2 years, or sooner if your vision changes
Practical Tips for Using Your Prescription
- Double-check SPH, CYL, and Axis before ordering
- Measure PD at home or use online tools
- Track eye exam dates for insurance coverage
- Keep a digital copy of your prescription for online orders
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Frequently Asked Questions (FAQ)
Can I order glasses online with only my prescription?
Yes! Make sure SPH, CYL, Axis, PD, and Prism are included for accurate ordering. Always confirm your PD.
What if my PD is missing from the prescription?
You can measure it at home with a printable ruler or ask your optometrist.
How often should I update my eyeglass prescription?
Eye exams are recommended every 1–2 years, or sooner if your vision changes.
