How to Read Your Eye Prescription for Glasses

Ever left the eye doctor's office holding a slip of paper covered in strange letters and numbers? You're definitely not the only one. An eye prescription simply tells you the exact lens power your eyes need to see clearly, using short codes like SPH, CYL, and ADD. Once you know what each one means, reading your own prescription feels almost simple. So what do all these codes actually stand for, and what do they say about your eyes?

What Is an Eye Prescription?

An eye prescription is a written order from your eye doctor. It tells you exactly what your eyes need to see clearly. Every prescription uses a standard format. Once you learn the layout, any eye chart becomes easy to read.

Quick Reference: What Every Abbreviation Means

Before we go deeper, here is a quick table. Use it to check your prescription at a glance.

This table is a fast way to check your eyeglass prescription without reading long paragraphs. Next, let us look closer at each term and what it means for your vision.

OD, OS, and OU: Understanding Which Eye Is Which

These three letters come from Latin. OD means your right eye. OS means your left eye. OU means both eyes together. Your prescription lists each eye in its own row.

Sphere (SPH): Your Main Lens Power

If you have a minus sign, you are nearsighted, also called myopia. A plus sign means that you are farsighted (hyperopic). The prescription strength is measured in diopters. The higher the number, the stronger the correction. The higher the number, the higher the prescription. Single-vision lenses are usually used when only an SPH value is provided (no ADD).

Cylinder (CYL) and Axis: Astigmatism Explained

CYL shows if you have astigmatism. This happens when your eye is more football-shaped than basketball-shaped. The axis number tells your optician where that curve sits. It is always between 1 and 180 degrees. If these fields are blank, you likely have no astigmatism at all.

Addition (ADD): Reading Power for Presbyopia

ADD appears on prescriptions for people over 40. It provides extra magnification for reading. This need is called Presbyopia. Progressives offer close and distance correction in a single lens and are virtually invisible if the ADD value is low. But others choose bifocals because the line makes it easy to find the reading area.

What Does Plano Mean on a Prescription?

Sometimes SPH shows Plano, written as PL. This simply means zero correction is needed for that eye. It is common and nothing to worry about.

Prism: Correcting Eye Alignment Issues

Prism is rare, but important when it appears. It corrects eye alignment problems, like double vision. The value tells your optician exactly how much correction your lenses need.

How to Read a Sample Prescription

Let's put it all together with a quick example.

OD: SPH -2.50, CYL -1.00, AXIS 090, ADD +2.00
This means your right eye is nearsighted, with mild astigmatism and reading power added.

OS: SPH -2.75, CYL Plano, AXIS blank, ADD +2.00
This means your left eye is nearsighted with no astigmatism.

Once you can read a sample like this, your own prescription becomes just as clear. If your prescription does not list a PD, you can measure it yourself using this PD measurement guide.

How Eye Prescriptions Change Over Time

Your vision often changes as you get older. One big change is something called presbyopia. This usually starts happening around age 40. 

That is why you should get your eyes checked regularly. If you sit in front of a computer or phone for a time, special lenses that block blue light can help your eyes feel better between checkups. Keeping your prescription up to date helps you choose the right eyeglasses whenever you're shopping for glasses in Canada.

FAQs

What does minus sign mean on eye prescription?

 A minus sign means you're nearsighted. Close objects look sharp, but far ones turn blurry. The larger the number, the more powerful the glasses.

Am I able to read my own eye prescription?

Yes, you can learn the basic skills on your own. But if there's anything you don't understand or don't see clearly, it's best to check with your eye doctor.

What is the difference between an eyeglass prescription and contact lens prescription?

 They aren't the same paper. Contact lenses need a few more details, including the base curve and diameter, which are determined during a contact lens fitting exam.

When should I have my prescription reviewed?

The majority of adults require an eye exam every 1-2 years. If your vision suddenly changes or feels off, go sooner!

Why isn't my PD listed on my prescription?

 Opticians often measure PD in person once you pick your frames. It's not always written down. You can also measure it yourself using a simple online guide.