How to Read & Understand Your Eyeglass or Contact Lens Prescription
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Stop squinting at those numbers—here’s what they actually mean.
Why This Matters
Your prescription isn’t just a jumble of numbers and abbreviations—it’s the key to clear, comfortable vision. Whether you're shopping for eyeglasses, contact lenses, or even just comparing options, understanding your RX will help you make smarter choices.
Prescription Basics: What's On That Paper?
A typical eyeglass or contact lens prescription includes:
| Abbreviation | What It Stands For | What It Means |
|---|---|---|
| OD | Oculus Dexter | Right Eye |
| OS | Oculus Sinister | Left Eye |
| OU | Oculus Uterque | Both Eyes |
| SPH | Sphere | Amount of nearsightedness (–) or farsightedness (+) |
| CYL | Cylinder | Astigmatism correction (shape of your eye) |
| AXIS | Axis | Orientation of astigmatism (0–180°) |
| ADD | Addition | Extra power for reading or multifocal lenses |
| PD | Pupillary Distance | Distance between your pupils (mm) |
| BC | Base Curve (for contacts) | Curve of the lens to match your eye |
| DIA | Diameter (for contacts) | Width of the contact lens |
| Brand | Brand-specific lenses | Required for contacts – not interchangeable |
Sample Eyeglass Prescription Explained
OD: -2.50 SPH | -1.00 CYL | AXIS 180
OS: -2.00 SPH | -0.75 CYL | AXIS 170
ADD: +1.50
PD: 63
What it means:
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You are nearsighted (negative SPH values).
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You have astigmatism in both eyes (CYL + AXIS values).
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You need reading help (ADD +1.50 = progressive or bifocal lenses).
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Your pupil distance is 63mm.
Contact Lens Prescriptions vs. Eyeglass Prescriptions
They’re not the same!
| Feature | Eyeglass Prescription | Contact Lens Prescription |
|---|---|---|
| Power (SPH, CYL, AXIS) | Yes | Yes |
| ADD | If multifocal or progressive | Yes (for multifocal contacts) |
| BC & DIA | Not included | Required to fit your eye curvature |
| Brand | Not specified | Must match approved lens brand |
| PD | Always needed for glasses | Not used for contacts |
You must get a separate exam for contacts—they sit on your eye, not in front of it like glasses.
Quick Tips to Read Your Prescription Like a Pro
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A minus SPH (–) means you're nearsighted (you see better up close).
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A plus SPH (+) means you're farsighted (you see better far away).
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If CYL and AXIS are listed, you have astigmatism.
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ADD is common in people over 40 for reading or computer work.
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Always double-check PD when ordering glasses online.
FAQs
Q: Can I use my eyeglass prescription to order contact lenses?
No — you need a specific contact lens prescription that includes brand, BC, and DIA.
Q: What does "Plano" mean on a prescription?
It means no correction needed for that eye (SPH = 0.00).
Q: What is a high prescription?
Generally, anything over ±4.00 SPH or more than –1.00 CYL for astigmatism is considered moderate to high.
Final Takeaway: Know Your Numbers
Understanding your prescription helps you:
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Order the right lenses
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Ask smarter questions at the optometrist
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Choose the right lens types & coatings