If you’ve recently had an eye exam and received a glasses prescription, you might wonder if you can use it to order contact lenses. While they seem similar, contact lens and eyeglasses prescriptions are not the same. They serve different purposes and are based on different measurements.

Understanding the differences can help you make informed decisions about your eye care and get the most accurate vision correction; especially if you rely on both glasses and contacts to get through your day.

Can I Get Contacts with My Glasses Prescription?

Glasses prescriptions measure how much correction your eyes need when lenses are placed in front of them; usually about 12 millimeters from the surface. Contact lenses sit directly on your eyes, which changes how the correction is calculated.

In lower prescriptions, there may be very little difference between glasses and contact lenses. But once your prescription exceeds around ±3.50 diopters, the difference becomes more noticeable. That’s because of something called vertex distance, the gap between your glasses and your eyes. Contact lenses require this difference to be factored into the power of the lens so your vision stays sharp.

It’s also important to remember that contact prescriptions include more than just power. They add:

• Base curve – to match the curvature of your cornea

• Diameter – for correct lens size and fit

• Brand or material – depending on what your eyes tolerate best

These additional values aren’t found on a glasses prescription, which is why you can’t use one interchangeably for both.

Convert Contact Prescription to Glasses (Or the Other Way Around)

It’s common to wonder if you can convert a contact lens prescription into a glasses one; or vice versa. While there are some general guidelines, it’s not a direct one-to-one swap.

From Contacts to Glasses

If your contact lens prescription is mild, the power for glasses may be nearly identical. But for higher prescriptions, the glasses power often needs to be adjusted upward. For example, a –6.00 diopter contact lens prescription might convert to about –6.50 for glasses.

That slight increase accounts for the distance glasses sit from your eyes, which changes how light enters. It may seem like a small change, but even a quarter of a diopter can impact visual clarity, especially for tasks like driving or reading signs at a distance.

From Glasses to Contacts

When moving from glasses to contact lenses, the opposite adjustment happens. A strong glasses prescription may need to be reduced slightly for a contact lens to work properly on the eye’s surface.

That said, even with accurate power conversions, you’d still be missing other crucial details, like the fit of the lens on your eye. So even if a chart gives you a rough estimate, a professional contact lens fitting is still necessary to prevent discomfort or blurry vision.

Why the 2 Prescriptions Are Different

A glasses prescription only needs to correct your vision at a distance. Since the lenses don’t touch your eyes, comfort and movement directly on your eyes aren’t part of the equation.

Contact lenses, on the other hand, need to:

• Stay in place without causing irritation

• Allow oxygen to pass through to your cornea

• Work with your blinking and tear film

• Fit the shape of your eye without sliding or drying out

This is why contact lens prescriptions include specific design features, and why trial fittings are often part of the process. For example, someone with dry eyes might need a particular lens material, while someone with a steep cornea might need a different base curve entirely.

Common Misconceptions

Many people believe that once they have a glasses prescription, they can just order contacts online. But without a proper fitting and evaluation, that decision can lead to:

• Discomfort

• Blurry or fluctuating vision

• Dryness or irritation

• Increased risk of infection

Even slight mismatches in lens size or shape can cause problems over time. Contact lenses that don’t fit properly can lead to corneal abrasions, inflammation, or serious infections. That’s why separate exams and measurements are necessary. Even 2 people with the same glasses prescription might need different contact lens types based on the shape and health of their eyes.

What to Do if You Need Both