Understanding Your Eyeglass Prescription: A Complete Beginner’s Guide

Introduction

If you’ve ever looked at your eyeglass prescription and wondered what all the letters and numbers mean, you’re not alone. Terms like SPH, CYL, AXIS, ADD, PD, and Prism can seem confusing if you’ve never ordered prescription glasses before.

The good news is that you don’t need to be an optician to understand the basics. Learning what each measurement means can help you feel more confident when ordering glasses online, checking your prescription, or discussing your vision with your eye care provider.

This guide explains every part of a standard eyeglass prescription in plain English. We’ll walk through each abbreviation, show you what a real prescription looks like, explain why each measurement matters, and answer some of the most common questions first-time buyers have.

By the end of this guide, you’ll understand how to read your prescription and know what information you’ll need when ordering prescription glasses from Choice Eyewear.

Quick Answer

An eyeglass prescription is a set of measurements used to create lenses that match your vision needs.

Most prescriptions include:

OD – Right eye
OS – Left eye
SPH – Amount of nearsightedness or farsightedness
CYL – Amount of astigmatism
AXIS – Direction of astigmatism
ADD – Additional power for reading or close-up vision
PD – Distance between the centers of your pupils
Prism – Correction for eye alignment when prescribed

Not every prescription includes every measurement. Blank fields are often completely normal and simply mean that particular correction isn’t needed.

Before You Begin

Before ordering prescription glasses, make sure you have a current eyeglass prescription from your eye care provider.

An eyeglass prescription is different from a contact lens prescription. Contact lens prescriptions include measurements for the lenses that sit directly on your eyes and generally cannot be used to make prescription eyeglasses.

If you’re unsure which prescription you have, contact your eye care provider before placing your order.

Understanding OD, OS, and OU

One of the first things you’ll notice on your prescription is a set of abbreviations identifying which eye each measurement belongs to.

OD (Oculus Dexter) – Right eye
OS (Oculus Sinister) – Left eye
OU (Oculus Uterque) – Both eyes

These are Latin abbreviations commonly used in eye care.

When entering your prescription online, always double-check that the values for your right and left eyes are entered in the correct places.

Diagram Placeholder: Sample prescription showing OD, OS, and OU.

What Does SPH Mean?

SPH (Sphere) measures the amount of lens power needed to correct nearsightedness or farsightedness.

A minus (-) number means you’re nearsighted (myopia), meaning distant objects appear blurry.

A plus (+) number means you’re farsighted (hyperopia), meaning close objects may be more difficult to see.

Examples:

SPH Value	Meaning
-1.25	Mild nearsightedness
-4.50	Moderate to strong nearsightedness
+2.00	Farsightedness
Plano (PL)	No spherical correction needed

As the number moves farther from zero, the prescription strength increases.

What Does CYL Mean?

CYL (Cylinder) measures the amount of astigmatism.

Astigmatism occurs when the front surface of the eye is shaped slightly differently than normal, causing light to focus unevenly.

Not everyone has astigmatism.

If your CYL box is blank, it usually means you don’t need this correction.

Examples:

CYL Value	Meaning
Blank	No astigmatism correction
-0.50	Mild astigmatism
-1.25	Moderate astigmatism
-2.50	Higher astigmatism

What Does AXIS Mean?

If your prescription includes a CYL value, it will also include an AXIS.

AXIS describes the orientation of your astigmatism and is measured from 1° to 180°.

It is not a measure of prescription strength.

For example:

CYL: -1.00
AXIS: 90°

Changing the AXIS can significantly affect how your glasses perform, so always enter it exactly as written.

What Does ADD Mean?

ADD stands for additional magnifying power used for reading or close-up tasks.

This value is commonly found on:

Progressive lenses
Bifocal lenses
Some reading prescriptions

If your prescription doesn’t include an ADD value, that’s completely normal.

Examples:

+1.00
+1.50
+2.25

The higher the ADD value, the more assistance your eyes need for close-up work.

What Is Pupillary Distance (PD)?

Pupillary Distance (PD) is the distance, measured in millimeters, between the centers of your pupils.

While PD isn’t part of your vision prescription, it’s essential for positioning the optical center of your lenses correctly.

An incorrect PD can affect comfort and clarity, especially with stronger prescriptions.

Many prescriptions include a PD measurement, but not all do. If yours doesn’t, your eye care provider may be able to provide it.

Diagram Placeholder: Illustration showing how PD is measured.

What Is Prism?

Some prescriptions include Prism to help correct eye alignment issues.

Prism lenses can help people whose eyes do not naturally work together as they should, reducing symptoms such as double vision in certain cases.

If your prescription includes Prism, you can enter the values directly during the ordering process on our website.

As with every prescription order, our team carefully reviews the information before production begins. If anything appears unclear or inconsistent, we’ll contact you before your lenses are made.

Sample Eyeglass Prescription

Below is an example of what a prescription may look like.

Eye	SPH	CYL	AXIS	ADD
OD	-2.25	-0.75	180	+2.00
OS	-1.75	-0.50	170	+2.00

PD: 63 mm

This example shows a person who is nearsighted, has mild astigmatism in both eyes, and uses progressive lenses for reading.

Common Prescription Terms

You may also see these abbreviations:

Term	Meaning
PL or Plano	No prescription power
DV	Distance Vision
NV	Near Vision
Rx	Prescription
OU	Both Eyes
OD	Right Eye
OS	Left Eye

Common Mistakes

Avoid these common mistakes when reading or entering your prescription:

Using a contact lens prescription instead of an eyeglass prescription.
Mixing up your right eye (OD) and left eye (OS).
Forgetting the plus (+) or minus (-) sign.
Typing the wrong AXIS number.
Guessing your PD instead of using an accurate measurement.
Leaving out your ADD value when it’s listed.
Assuming a blank CYL means something is missing—it often means you don’t have astigmatism.
Entering Prism values in the wrong direction.
Using an expired prescription.
Waiting until production begins before reporting an error.

Frequently Asked Questions

Is my contact lens prescription the same as my eyeglass prescription?

No. Contact lens prescriptions contain additional measurements and generally cannot be used for eyeglasses.

Why is my CYL blank?

A blank CYL field usually means you don’t need astigmatism correction.

What does a minus (-) SPH value mean?

A minus value indicates nearsightedness (myopia).

What does a plus (+) SPH value mean?

A plus value indicates farsightedness (hyperopia).

What if my prescription includes Prism?

You can enter Prism values directly on our website. If we have any questions after reviewing your prescription, we’ll contact you before production begins.

What if my prescription doesn’t include a PD?

Ask your eye care provider if they can provide it, or see our guide on measuring your Pupillary Distance.

Why do my right and left eyes have different numbers?

It’s very common for each eye to require a different prescription.

Can I reuse an old prescription?

You should use your most current prescription unless your eye care provider has advised otherwise.

What does Plano (PL) mean?

Plano means no spherical correction is needed for that eye.

Can I enter my prescription manually?

Yes. During checkout, you can either upload your prescription or enter the values manually. Just be sure to copy each number exactly as it appears.

Key Takeaways

Your eyeglass prescription contains the measurements needed to create lenses tailored to your vision. While the abbreviations may seem technical at first, understanding what SPH, CYL, AXIS, ADD, PD, and Prism represent makes it much easier to order glasses confidently and accurately.

If you’re ever unsure about your prescription, don’t guess. Contact your eye care provider or reach out to our team—we’re happy to review your information and help ensure your order is correct.

Related Guides

How to Order Prescription Glasses
How to Measure Your Pupillary Distance (PD)
Lens Options Explained
Choosing the Right Eyeglass Frames
Progressive vs. Single Vision Lenses

Need More Help?

Still have questions about your prescription? Contact the Choice Eyewear team, and we’ll be happy to help you understand your prescription and guide you through the ordering process.