How to Read Your Eyeglass Prescription: What Do All Those Letters and Numbers Really Mean?

You just had your annual eye exam and handed over your prescription to your optician, excited to pick out the perfect new pair of glasses. But when you glance at the prescription, it looks like a jumble of numbers, symbols, and abbreviations. What does it all mean?

Understanding your eyeglass prescription can give you useful insight into your vision and eye health. Let’s break it down in simple terms.
 

What Do OD, OS, and OU Mean?

Your prescription is often written in a grid using abbreviations, many of them derived from Latin:

• OD – Oculus Dexter, or your right eye
• OS – Oculus Sinister, or your left eye
• OU – Oculus Uterque, meaning both eyes

These terms help differentiate vision needs for each eye.
 

SPH (Sphere): Nearsighted or Farsighted?

The “Sphere (SPH)” column refers to the lens power you need to correct nearsightedness or farsightedness, measured in diopters (D).

• A minus sign (-) means you're nearsighted—you see better up close than far away.
• A plus sign (+) means you're farsighted—you see better far away than up close.

The word “sphere” indicates that the correction is uniform in all directions. To visualize it, imagine slicing a glass ball; the curve is the same all the way around—hence the spherical shape.
 

CYL (Cylinder) and AXIS: Correcting Astigmatism

If you have astigmatism, your cornea isn't perfectly round—it's more like a football than a basketball. This causes vision to blur or distort at any distance.

• CYL (Cylinder): This measures the amount of correction needed for astigmatism.
• AXIS: This indicates the orientation of that correction, measured in degrees from 1 to 180. Think of it like a protractor superimposed on your eye.

If no cylinder value appears, you likely don’t have astigmatism.
 

ADD: Help for Reading and Near Vision

If your prescription includes an ADD value, it means you need extra magnifying power in the lower part of your lenses to help with near tasks like reading. This is common in multifocal or progressive lenses, especially for those over age 40. ADD values typically range from +0.75 to +3.00 D and are the same for both eyes.
 

PRISM: Correcting Eye Alignment

In rare cases, your doctor may add a PRISM correction to address eye alignment issues (such as double vision). This is not common, but it helps guide light properly if your eyes don’t work together as they should.
 

A Sample Prescription

Here’s what a typical prescription might look like:

OD -2.00 SPH +2.00 ADD
OS -1.00 -0.50 x 180 +2.00 ADD

This means:

• The right eye (OD) is nearsighted with no astigmatism and has a +2.00 ADD for reading.
• The left eye (OS) is also nearsighted with mild astigmatism (-0.50 at 180°) and the same +2.00 ADD for near vision.

Glasses vs. Contact Lens Prescriptions

It’s important to know that an eyeglass prescription is not the same as a contact lens prescription.
Eyeglasses sit a short distance from your eyes, while contact lenses rest directly on your cornea. Because of this, contact lens prescriptions must also include:

• Lens base curve
• Diameter
• Brand and manufacturer

An accurate contact lens prescription can only be provided after a fitting and follow-up evaluation by your eye doctor.
 

Keep Your Vision in Focus

Nearly 75% of people need some form of vision correction—and that number increases with age. To ensure you're seeing clearly, make your annual eye exam a part of your regular health routine. An up-to-date prescription helps ensure you're getting the best lenses for your unique eyes.

At Eye Associates, we’re proud of the long-term relationships we build with our patients and the quality care we provide.

Contact us today to schedule your exam. Life looks better in focus—let us help you see the clarity.

The information in this article should not be used for medical advice, diagnosis or treatment. As always, you should consult with your health care provider about your specific health needs.