Can You Use a Glasses Prescription for Contacts?

What you need to know about your eyewear prescriptions and how they differ

Co-authored by David Felsted, DO and Aly Rusciano

Last Updated: March 24, 2023 References

Glasses vs. Contacts

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Converting a Glasses Prescription

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Using the Same Prescription

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Contact Lens Specifics

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Tips

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Warnings

So, you have glasses but want contacts. We get it—eye accessories don’t match every occasion! But the only problem is you don’t want to go back to the optometrist. You’ve already had your eyes checked and have the glasses prescription; you should be able to use that to get contacts, right? Well, not exactly. In this article, we’ll explain the whys and hows behind whether using your eye prescriptions interchangeably is really possible.

Things You Should Know

Glasses and contact lens prescriptions cannot be used interchangeably because they’re 2 different prescriptions.
Converting the vertex distance of a glasses prescription can help you determine how different a contacts prescription would be.
Visit an optometrist to safely find your contact lens prescription so you don’t damage your sight.

Section 1 of 4:

Are glasses and contacts prescriptions the same thing?

No, the prescriptions for glasses and contacts are different. Because glasses sit away from your eyes and contacts rest on your eyes, their prescription are not the same. Different measurements and tests go into both prescriptions and using prescriptions interchangeably won’t give you the same visual acuity.^{[1]
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- Visual acuity measures how well an eye can recognize shapes and details at a given distance.^{[2]
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- Unlike glasses, contact lens prescriptions include the base curve and diameter of the eye, along with the needed lens material and brand/manufacturer.

Section 2 of 4:

Converting a Glasses Prescription

Estimate the vertex distance to convert your glasses to contacts. Vertex distance measures the space between the back of a lens and the eye.^{[3]
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Research source} Look at your glasses prescription and note the lens power. Then, find it on the above chart under one of the glasses power columns. If the difference in power between your glasses power number and the adjacent contact lens power number is less than 0.25, you might have a similar prescription in both glasses and contacts.^{[4]
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- Now, this isn’t to say you should use the same prescription for glasses and contact lenses. This should only be used in an emergency case, like when you can't get ahold of your eye doctor.
- This chart won't work if you have astigmatism because your cornea is shaped differently.

Section 3 of 4:

What happens if you use the same prescription?

Using the same prescription will throw off your vision. To put it simply, glasses and contact lens prescriptions should not be used interchangeably. Even if you wear contacts and glasses, your prescriptions can be very different.^{[5]
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- The eye exams for glasses and contacts are also different, which is another reason why the prescriptions shouldn’t be used interchangeably, as the measurements and tests are not the same.^{[6]
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Section 4 of 4:

Contact Lens Prescription Specifications

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Base curve The base curve determines the form and shape of your contacts. Optometrists will measure your eye to make sure the lens matches your eye’s shape and size. Basically, the base curve is the dome shape of the lens.^{[7]
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- A glasses eye exam and prescription doesn’t include this measurement because glasses sit away from your eye and don’t need to rest perfectly against your cornea.
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Diameter The diameter is the overall size of the contacts. It measures how long the contact needs to be from edge to edge.^{[8]
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- Remember learning about radius and diameter in math class? Well, the diameter of a contact lens is the same thing!
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Lens material The lens material determines what your contacts are made of. Unlike glasses, contacts are made with various hydrogels. Some are made with strictly hydrogel, while others use a combination of hydrogel and silicone. Your optometrist will prescribe whatever best matches your needs.^{[9]
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- Hydrogel is a thin and malleable gel-like water-containing polymer that’s typically used to make disposable contact lenses.
- Silicone hydrogel lenses are ideal for dry eyes because they allow more oxygen into the eye.
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Brand/manufacturer The brand/manufacturer states what company your contacts are from. An optometrist may recommend one brand of contacts over another for your specific needs. The manufacturer can play a big part in how a contact lens is made.^{[10]
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- Unlike glasses, contact lens brands are not equal. Different brands can have different base curves and diameters, so each prescription is specific to a given brand.

Warnings

While conversion charts and tools can help you find a contact lens prescription at home, it’s always best to go to an eye doctor and get a separate exam, especially before buying contacts.

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