How to Read an Eyeglass Prescription (Simple Guide for Beginners)

Trying to understand your eyeglass prescription after an eye exam can feel like you need a second prescription just to read it. Your optometrist hands you a page full of abbreviations, numbers, and symbols — and unless you’re in the optical world, it can look like another language.

The good news? Reading your eyeglasses prescription is easier than you think once you know what each part means. This guide breaks down SPH, CYL, Axis, Prism, PD, and more so you can confidently order your prescription glasses online in Canada or the USA.

Why Understanding Your Eyeglass Prescription Matters

Your eyeglass prescription tells the optical lab exactly how to cut your lenses so you can see clearly. It includes:

• Your level of nearsightedness or farsightedness
• Whether you have astigmatism
• Whether you need reading/add power
• Your pupillary distance (PD)
• Any prism correction

Your glasses prescription is ONLY for eyeglasses — it does not include the extra measurements required for contact lenses. If you wear contacts, you must get a separate contact lens prescription.

What Do All the Letters and Numbers Mean?

Your eyeglass prescription will include several key measurements. Here’s what each one means:

Sphere (SPH):

The SPH correction tells you how strong your lens needs to be to correct your overall vision.

• A minus (-) sign = nearsightedness (myopia)
• A plus (+) sign = farsightedness (hyperopia)

Examples:

• -1.00 means you need 1 diopter of correction for nearsightedness.
• +2.50 means you need 2.50 diopters for farsightedness.

The higher the number, the stronger the correction.

Cylinder (CYL):

The CYL value shows how much astigmatism correction you need.

If this box is empty, you don’t have astigmatism.

Axis:

The Axis appears only when a CYL value is present.

It tells the lab the angle (1–180 degrees) where the astigmatism correction should be placed.

Without axis, the astigmatism cannot be corrected properly.

Prism:

Prism is used to correct eye-alignment issues such as double vision.

It is measured in prism diopters (p.d.). Only a small percentage of prescriptions include prism.

Common prism directions:

• BO – Base Out
• BI – Base In
• BU – Base Up
• BD – Base Down

Other Prescription Abbreviations (Glossary)

• ADD – Extra magnifying power for reading, bifocals, and progressive lenses
• DV – Distance Vision
• NV – Near Vision
• OD – Right eye (Oculus Dexter)
• OS – Left eye (Oculus Sinister)
• OU – Both eyes
• PD – Pupillary Distance (distance between your pupils)
• Monocular PD – PD for each eye
• Binocular PD – Combined PD

This information ensures your lenses are centered properly for the sharpest vision.

How to Read a Glasses Prescription (Step-by-Step)

1.

Look at SPH

Tells you if you’re near- or farsighted.

2.

Check CYL and Axis (if you have astigmatism)

These work together to correct astigmatism.

3.

Check ADD

If present, you need reading or progressive lenses.

4.

Review PD

Essential for ordering glasses online — it tells us where to center the lenses.

5.

Match these numbers when ordering online

When buying glasses on SeeClearOptical.com, simply enter the numbers exactly as they appear on your prescription.

Example Prescription Explained

Right Eye (OD):

• SPH: -2.50
• CYL: -0.75
• Axis: 173
• ADD: +2.25

This means the right eye is nearsighted with astigmatism and needs reading power for multifocal lenses.

Left Eye (OS):

• SPH: -3.00
• CYL: -1.00
• Axis: 004
• ADD: +2.25

This eye is also nearsighted with astigmatism and requires the same reading power.

Without ADD, this would be a single-vision prescription.

How often should you get an eye exam?

If you don’t have any medical issues that affect your vision, you should have a comprehensive eye exam every one to two years.

Order Your Prescription Glasses Easily at SeeClear Optical

At SeeClear Optical, we make it easy to read your prescription and order affordable glasses online.

We offer:

• Stylish frames for men & women
• High-index thin lenses for strong prescriptions
• Progressive, bifocal, and single-vision lenses
• Anti-reflective & blue-light coatings
• Direct billing options
• Fast shipping across Canada & USA

If you’re unsure how to enter your prescription, our licensed opticians are here to help you every step of the way.