How to Read Your Eyeglass Prescription

You just got your eyes tested and walked out with a slip of paper full of numbers and abbreviations. Here's what it all means — no jargon, no fluff.

TL;DR: Your eyeglass prescription has three key numbers — SPH (lens strength), CYL/AXIS (astigmatism), and PD (pupil distance). Contacts and Ortho-K lenses use different prescriptions entirely.

Part 1: Eyeglass Prescription

This is the prescription you use for frames. It's the most common one, and it looks something like this:

Here's what each number means:

• SPH (Sphere) — your main prescription strength

This is how nearsighted or farsighted you are. A minus sign (−) means nearsighted; a plus sign (+) means farsighted. The bigger the number, the stronger the prescription.

• CYL + AXIS — your astigmatism

CYL is how much astigmatism you have. AXIS is the direction of it, measured in degrees. These two always go together — if CYL is blank, you have no astigmatism.

• PD (Pupillary Distance) — the most important number for frames

This is the distance between your pupils in millimeters. When lenses are cut for your frames, the optical center needs to line up exactly with your pupils. Even a small error here can cause headaches or eye strain. Make sure this number is on your prescription — if it's missing, ask your optometrist for it.

• ADD — only if you need reading glasses or progressive lenses

If you're over 40 and need help with close-up vision, you'll see an ADD value (e.g., +1.50). This tells the lab how much extra reading power to add to the bottom of the lens. Frames with progressives need to be tall enough to fit the full lens — we can help you pick the right ones.

Want to learn more about how progressive lenses work? [Read our guide here.]

• VA and Prism — you probably don't need to worry about these

VA (visual acuity) is just a record of how well you see with the prescription — it's not something you need to do anything with. Prism only shows up in prescriptions for eye alignment issues and is fairly uncommon.

Part 2: Contact Lens Prescription

Your contact lens prescription is a separate document from your glasses prescription. You cannot use one in place of the other.

The main difference: glasses sit about half an inch in front of your eye, while contacts sit directly on your cornea. This changes the lens power needed, especially for stronger prescriptions.

On top of the usual SPH and CYL values, a contact lens prescription will include:

• BC (Base Curve) — the curvature of the lens, so it fits the shape of your eye
• DIA (Diameter) — the width of the lens
• Brand — contacts are fit to specific products, not just measurements

If you wear contacts and want to get frames too, bring both prescriptions. We work from the glasses Rx for your lenses.

Part 3: Ortho-K Prescription

Ortho-K (orthokeratology) lenses are worn overnight to gently reshape your cornea while you sleep. In the morning, you remove them and can see clearly without glasses or contacts for the rest of the day.

These are mostly used for myopia control in kids and teens, or for adults who want to go glasses-free during the day without surgery.

The prescription for Ortho-K is the most technical of the three — it includes multiple lens zone measurements and is based on a detailed map of your cornea. It can only be used for Ortho-K lenses, not for glasses or regular contacts.

If your child wears Ortho-K and also needs a backup pair of glasses, bring their optometrist's report and we'll sort it out.

The One Thing to Remember

All three prescriptions are different documents and cannot be swapped. Your glasses Rx is only for glasses. Your contact lens Rx is only for contacts. Your Ortho-K Rx is only for Ortho-K lenses.

Still not sure about something on your prescription? Bring it in — we're happy to take a look with you.

Frequently Questions Asked (FQA)

• How do I read my glasses prescription?

Look for SPH (your main lens strength), CYL and AXIS (astigmatism, if any), and PD (pupillary distance). SPH with a minus sign means nearsighted; plus means farsighted. The rest of this article walks through each number in detail.

• What does −0.75 mean on a glasses prescription?

It means mild nearsightedness — you have a little difficulty seeing things clearly at a distance. The minus sign tells you it's nearsightedness, and 0.75 is a relatively low prescription strength.

• What does ADD mean on a prescription?

ADD stands for addition — it's the extra reading power added to your lens for close-up vision. You'll only see it if you need progressive or bifocal lenses, usually from your mid-40s onward. The higher the ADD value, the more reading power is built into the lens.

• What is PD and why does it matter?

PD (pupillary distance) is the measurement between your two pupils in millimeters. It tells the lab exactly where to center the optical power in each lens. If the PD is off, even by a small amount, it can cause eye strain or headaches — so it's worth double-checking before you order.

• Can I use my glasses prescription for contact lenses?

No. They're two separate prescriptions and can't be swapped. Contacts sit directly on your eye, which changes the power needed. A contact lens prescription also includes additional measurements (base curve and diameter) that your glasses prescription doesn't have.

Got Questions? We’re Here to Help. If you have any inquiries or need assistance selecting the perfect lens, please feel free to reach out to us at support@migafas.com.

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The contents of this blog post are for informational and marketing purposes only.
This content is not medical advice and should not be considered professional health care advice, diagnosis, or treatment.
MiGAFAS does not provide medical, optometric, or professional health care services.
Always seek the advice of your optometrist or other qualified health provider for all medical advice, diagnosis, treatment, or questions regarding a medical condition.