How to Read Your Eyeglass Prescription

If you’re new to wearing eyeglasses or your vision has recently changed, you might be curious about how to read your eyeglass prescription. There’s a lot more than just the expiration date to know about. But don’t worry, it’s not as complicated as it seems.

This beginner’s guide will help you understand each element of your glasses prescription, making it easier for you to make informed decisions about your eye care.

eyeglass prescription example chart with lines indicating which eye is right (OD) and which eye is left (OS)

In this article, we’ll break down the various components of an eyeglass prescription, from the abbreviations and numbers to their meanings. By the end, you’ll be able to read your prescription like a pro and confidently discuss it with your eye care professional.

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OD and OS

The first thing you’ll notice on your prescription are the terms “OD” and “OS.” OD stands for “oculus dexter,” which is Latin for the right eye, while OS stands for “oculus sinister,” or the left eye. These abbreviations tell you which eye each part of the prescription refers to.

Tp put it simply:

  • OD = Right Eye
  • OS = Left Eye

Your eyes might have different prescriptions, and it’s important to know which one is for the right and left eye. So just remember, OD is for the right eye, and OS is for the left eye.

What does Sphere (SPH) mean?

The Sphere (SPH) number on your prescription represents the amount of lens power needed to correct your vision, specifically for nearsightedness or farsightedness. A positive (+) number means you are farsighted (hyperopia), and a negative (-) number indicates you are nearsighted (myopia).

For example, if your SPH number is -2.00, you have nearsightedness. As a result, your lenses will be shaped to help you see distant objects more clearly.

On the other hand, if your SPH number is +2.00, you are farsighted, and your lenses will help you see close-up objects better.

What is the Cylinder (CYL) number on my prescription?

The Cylinder (CYL) number on your prescription is crucial if you have astigmatism, a common condition where the cornea has an irregular shape. This irregularity causes blurred vision at any distance. Therefore, the CYL number measures the amount of lens power needed to correct astigmatism.

CYL is also expressed in diopters (D). Just like the SPH number, the CYL number can be either positive or negative. A higher number indicates a higher degree of astigmatism that needs correction.

Do you have astigmatism? If so, you can learn more about our specialty contact lenses to find out if they might be a better option for you.


The axis, measured in degrees, indicates the orientation of the astigmatism correction in your lenses. This number ranges from 1 to 180, with 90 representing the vertical meridian and 180 representing the horizontal meridian.

The axis measurement is essential to ensure that your lenses are positioned correctly in your eyeglasses. With a proper axis measurement, your doctor will be able to provide the best possible vision correction for you.


The “Add” number on your prescription is relevant for those who need multifocal lenses, such as bifocals or progressive lenses. It represents the additional power needed for near vision, helping you see up-close objects clearly.

This number is always positive and typically ranges from +0.75 to +3.00 D. The Add number is the same for both eyes in most cases.


A prism measurement on your prescription is less common. Doctors use this measurement to correct eye alignment issues, such as double vision or strabismus.

On your eyeglass prescription, prism values may have one or more of the following column names:

  • Base (or Base Curve)
  • H (Horizontal or Hz)
  • V (Vertical or VT)

This measurement indicates the amount of prism needed to help your eyes work together properly. The H and V values tell you which direction the prism needs to be faced.

Can you use your eyeglass prescription to buy contact lenses?

No, unfortunately you can’t use your eyeglass prescription to buy contact lenses. Although eyeglass and contact lens prescriptions contain similar information, they are not interchangeable.

Contact lenses sit directly on the eye, so their measurements and fitting process differ from eyeglasses. Therefore, it’s crucial to consult your eye care professional to obtain a separate prescription for contact lenses.

If you want to order contact lenses, your eye doctor will perform a contact lens fitting to determine the best type and size of lenses for your eyes. They will then provide you with a contact lens prescription, which you can use to purchase the appropriate lenses.


In conclusion, understanding your eyeglass prescription is essential to ensure you get the right corrective lenses for your vision needs. In this blog post, we’ve covered the various components of an eyeglass prescription, including OD and OS, Sphere, Cylinder, Axis, Add, and Prism.

Remember that eyeglass prescriptions and contact lens prescriptions are not the same, so always consult your eye care professional for the correct prescription. You also want to make sure that your eyeglass prescription is not expired, otherwise you’ll need to undergo a new exam.

If you have any questions or concerns about your eyeglass prescription, the knowledgeable and friendly team at Eye Society is here to help. Dr. Tanvi Mago and her team of experienced eye care professionals provide high-quality eye care services for patients young and old.

Don’t hesitate to schedule an appointment with Dr. Tanvi Mago at Eye Society in Chicago, IL. Your eye health and vision is our priority, and we’ll do whatever it takes to ensure you can see clearly and comfortably. Call us today to book your eye exam appointment and get the expert care you deserve.

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