Are Glasses & Contact Prescriptions the Same?

Picture this: you’re picking up a new pair of glasses and ask to add on some contact lenses to your purchase. Would you be surprised to hear you can’t get them without another full eye exam? Confusion is understandable; you have a glasses prescription in hand! What’s the issue? Whether you’re looking for glasses or contacts, your eyes and vision are the same in both situations—shouldn’t the prescriptions be the same too?

Unfortunately, transferring your prescription between contacts and glasses isn’t that simple. The team at EyeRx is here to help uncover the difference between glasses and contact prescriptions. Let’s explore how to read the prescription for either.


The difference in contact lenses and glasses prescriptions comes down to how the visual aid is used. Though glasses and contacts both offer better, clearer vision and even use similar methods, the few millimeters between where these corrective lenses operate makes a huge difference.

Since glasses are set in front of your eyes, the distance between the eye’s surface and the lens affects the strength of your prescription. Glasses are custom fit to your face, of course, but there are fewer variables in how they suit your eyeball itself.

Contact lenses, on the other hand, sit directly on the eye, resting on the cornea. The precise curve of your eyeball, the thickness and volume of your tears, and the unique shape of your eye are all critical components of how your contacts correct your vision.


Vision is measured in diopters, which measure the focusing power in the lens of your eye. The smaller the number in your prescription is, the less correction is needed. The higher the number listed, the stronger your lens prescription will be.


Reading a glasses prescription can feel like reading another language—and sometimes it is! Latin isn’t uncommon in prescriptions, and, as with any specialized field, the abbreviations and terminology can be confusing to someone who doesn’t work with them day in and day out.

We’ve broken down some of the abbreviations you’ll find in your glasses prescription. The list below can help clarify what each set of letters, numbers, and symbols means:

  • OD—Oculus dexter, which refers to your right eye

  • OS—Oculus sinister, which refers to your left eye

  • OU—Oculus uterque, or both eyes

  • SPH—sphere, which is the power of the lens that will correct your eyesight

  • (+)— the positive sign in your prescription before the sphere number denotes correction of hyperopia (farsightedness)

  • (-)—the negative sign in your prescription before the sphere number denotes correction of myopia (nearsightedness)

  • CYL—cylinder, which measures the amount of astigmatism in your eye, if any

  • Axis—a number between 1 & 180 that signifies where the astigmatism is in the eye

  • ADD—used for reading glasses or bifocals, the ADD number signifies how strong any additional corrective areas of the lens should be

  • Prism—indicates if you need prismatic correction added to the lenses to address double vision

Not every prescription will have all of these components. Remember, if you have any questions about your prescription, your vision, or any part of your eye exam, your eye doctor is there to help you. Please ask for any clarification you need.


If you’re after contact lenses, you’ll need to book some extra time for your exam since you’ll undergo a comprehensive eye exam as well as some special tests specifically for your contact lenses.

It’s necessary to have a contact lens exam to ensure your contacts fit correctly. Your prescription will include the corrective information from your glasses prescription, as well as:

  • BC—Base curve, this measures the curvature of your cornea & helps make sure your contacts have a comfortable fit

  • DIA—Diameter, specifically the diameter of the lens needed to cover the cornea appropriately 

  • Type of contact lens material

  • Brand of contact lens

Even the type and brand are crucial parts of the prescription—that’s why you’ll have a dedicated contact fitting to find the contacts that are most comfortable for your unique eyes.


If you choose to wear contacts, you will still need to have a pair of glasses, so you’ll need prescriptions for both.

Contact lenses are fantastic, but in the event you develop irritated or dry eyes or come down with an eye infection, you’ll need to give your eyes a rest. Glasses are a better choice in this case since they don’t sit directly on the eye’s surface. This can give your eyes the time they need to heal.

If you’d prefer only to have glasses, you won’t require the testing and measurements needed for a contact lens prescription.


You can have the best of both worlds. Get your contact lens prescription and glasses prescriptions at EyeRx and see the world your way. Please book an appointment soon and let us know what type of prescription you require so we can tailor your exam to your exact needs.

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