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Are Contact Lens Prescriptions the Same as Glasses?

Ever wondered if you can use your glasses prescription to order contact lenses? It seems logical—both correct your vision, right?

But the truth is, contact lens prescriptions are NOT the same as glasses prescriptions. They’re not interchangeable. While they serve the same purpose, glasses and contact lens prescriptions have different measurements, specifications, and requirements. Here’s what you need to know before making the switch.

Contact Lens Prescription vs. Glasses Prescription: What’s the Difference?

A glasses prescription and a contact lens prescription may look similar at first glance, but they include different details. Here’s how they compare:

1. Lens Positioning

Your glasses sit about 12 millimeters from your eyes, while contact lenses rest directly on the cornea. This difference affects how the lens power is calculated. Higher prescriptions often require adjustments when switching between glasses and contacts because of the way light bends through the lenses.

2. Additional Measurements for Contact Lenses

Unlike glasses, contact lenses require extra specifications for a proper fit:

  • Base Curve (BC): Determines how well the lens sits on your eye. Too flat or too steep, and you could experience discomfort or poor vision.
  • Diameter (DIA): Affects how the lens covers your cornea. The wrong size can cause irritation or movement issues.
  • Lens Material & Brand: Some prescriptions specify a particular brand or material to match your eye’s oxygen needs and moisture levels. Browse our collection of reputable contact lens brands today.

3. Vision Adjustments

Because contacts sit directly on your eye, the power needed to correct your vision might be different than what’s written in your glasses prescription. This is especially important for people with strong prescriptions. Your eye doctor will make these adjustments when fitting you for contacts.

Why You Need Separate Eye Exams for Each

Thinking about skipping the contact lens exam and using your glasses prescription instead? Not a great idea. Here’s why:

Proper Fit is Essential

Glasses don’t require much fitting—once the lenses match your prescription, you’re set. Contacts, however, must be measured to fit the unique shape of your eye. A poorly fitting lens can cause discomfort, blurry vision, or even eye infections.

Eye Health Checks for Contacts

Wearing contact lenses increases your risk of dry eyes, infections, and corneal damage. A contact lens exam includes tests to ensure your eyes can handle lenses safely.

Legal and Safety Requirements

In most places, you can’t legally purchase contact lenses without a valid prescription from an eye doctor. This rule exists to protect your vision and prevent damage from ill-fitting or expired lenses.

How to Read a Contact Lens Prescription

If you’ve received a contact lens prescription, it includes more details than your glasses prescription. Here’s how to decode it:

  • OD (Right Eye) / OS (Left Eye): Indicates the prescription details for each eye.
  • Power (PWR or SPH): The strength of the correction needed.
  • Base Curve (BC): Ensures the lens fits the curvature of your eye.
  • Diameter (DIA): Defines the lens size.
  • Cylinder (CYL) and Axis (for Astigmatism): If you have astigmatism, these values correct the irregular shape of your cornea.
  • Add Power (ADD, for Multifocal Lenses): Provides additional correction for reading.
  • Brand Name: Contact lens prescriptions often specify an approved brand or material.

Does a Contact Lens Prescription Expire?

Yes! Most contact lens prescriptions expire after one year. Some states allow prescriptions to last up to two years, but the FDA and most eye care professionals recommend annual check-ups.

Why? Your eye shape, vision, and overall eye health can change. Regular exams ensure your lenses still fit well and don’t cause harm.

Here’s a breakdown of how long different states allow contact lens prescriptions to remain valid:

StateExpiration Period
Alabama1 year
Alaska2 years
Arizona1 year
Arkansas1 year
California2 years
Colorado1 year
Connecticut1 year
Delaware1 year
Florida2 years
Georgia1 year
Hawaii1 year
Idaho2 years
Illinois1 year
Indiana1 year
Iowa1 year
Kansas1 year
Kentucky1 year
Louisiana1 year
Maine2 years
Maryland1 year
Massachusetts1 year
Michigan1 year
Minnesota2 years
Mississippi1 year
Missouri1 year
Montana2 years
Nebraska1 year
Nevada1 year
New Hampshire1 year
New Jersey2 years
New Mexico1 year
New York1 year
North Carolina1 year
North Dakota2 years
Ohio1 year
Oklahoma1 year
Oregon2 years
Pennsylvania1 year
Rhode Island1 year
South Carolina1 year
South Dakota2 years
Tennessee1 year
Texas1 year
Utah2 years
Vermont1 year
Virginia1 year
Washington2 years
West Virginia1 year
Wisconsin2 years
Wyoming1 year
How long a contact lens prescription lasts in every U.S. state

TL;DR: Contact Lens Prescription Is Not the Same as Glasses Prescription

Think your glasses prescription will work for contact lenses? Think again. Contacts sit directly on your eye, meaning they require specific measurements like base curve and diameter for a safe and comfortable fit. That’s why you need a separate prescription tailored just for them.

When buying contacts, don’t gamble with your vision. Stick with trusted retailers like Contacts America to guarantee you’re getting authentic, FDA-approved lenses. Your eyes deserve nothing short of the best.

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