If you’ve ever worn both glasses and contact lenses, you might have noticed that the prescriptions aren’t the same. Even though both correct vision, they use different measurements and specifications based on how they sit on your eyes.
Glasses sit about half an inch away from your eyes, while contact lenses rest directly on the cornea. That difference may not seem like much, but it changes how light enters the eye, meaning that your prescriptions are not interchangeable.
Are Contact and Glasses Prescriptions the Same?
No, they’re not the same. A contact lens prescription includes extra measurements to ensure the lenses fit properly on the eye. A glasses prescription, on the other hand, is based on how light passes through lenses positioned slightly away from the eyes.
This means you can’t just take your glasses prescription and order contact lenses—it won’t work. Instead, you need a separate contact lens exam and fitting to make sure the lenses match the shape of your cornea and provide you with the right correction.
What’s in a Contact Lens Prescription?
A contact lens prescription includes measurements that ensure a comfortable, secure fit. Here’s what it includes:
- Power (SPH) – The strength needed to correct nearsightedness or farsightedness.
- Base curve (BC) – The curve of the lens, ensuring it fits the cornea properly.
- Diameter (DIA) – The size of the lens to match your eye’s shape.
- Lens brand or material – Contacts come in different materials, each offering different levels of oxygen flow and moisture retention.
- Cylinder (CYL) & Axis – These are needed for toric lenses, which correct astigmatism.
- Add Power (ADD) – Used for multifocal or bifocal contacts to correct presbyopia.
Why Does Fit Matter?
Unlike glasses, which don’t touch the eye, contact lenses need to fit precisely. If a contact lens is too tight, it can cause discomfort, reduce oxygen flow, and even lead to corneal damage. If it’s too loose, it can move around, leading to blurry vision and irritation.
What’s in a Glasses Prescription?
A glasses prescription focuses only on visual correction and doesn’t include measurements related to fit. It typically includes:
- Power (SPH) – Just like in a contact lens prescription, this corrects nearsightedness or farsightedness.
- Cylinder (CYL) & Axis – If you have astigmatism, these measurements help correct it.
- Prism – Used to correct alignment issues in some patients.
- Pupillary Distance (PD) – The distance between your pupils, ensuring that the glasses’ lenses align properly.
Since glasses rest away from your eyes, they don’t require curvature, diameter, or material specifications like contact lenses do.
Why Do You Need a Separate Exam for Contacts?
A glasses prescription isn’t enough to get contact lenses because it doesn’t include corneal measurements or a lens fitting.
A contact lens exam ensures:
- The lens fits your cornea’s shape.
- Your eyes get enough oxygen flow.
- The lenses provide clear vision without causing irritation.
What Happens During a Contact Lens Exam?
A contact lens exam goes beyond a standard vision test. Since contact lenses sit directly on the eye, they require precise measurements to ensure a proper fit, clear vision, and all-day comfort. A contact lens exam helps determine the best lens type, material, and prescription for your unique eye shape and needs.
Here’s what you can expect during the fitting process:
- Corneal measurements – Your doctor maps the shape of your cornea to find the right fit.
- Tear film evaluation – This checks if your eyes produce enough moisture for comfortable lens wear.
- Trial lenses – You’ll get a trial pair to test for fit, clarity, and comfort.
- Prescription finalization – Once the perfect fit is found, your doctor will finalize your prescription.
Skipping this process can lead to discomfort, blurry vision, or even eye infections.
What Happens If You Use a Glasses Prescription for Contacts?
If you try to order contact lenses using a glasses prescription, you may experience:
- Blurry vision – Glasses and contacts focus light differently, so your vision may not be as clear.
- Poor fit – Contact lenses must match your eye’s shape. A bad fit can lead to irritation, redness, and dryness.
- Increased risk of infection – Ill-fitting lenses can reduce oxygen flow, leading to eye infections and discomfort.
Using the right prescription for the right lens type helps protect both your vision and eye health.
Can Everyone Wear Contact Lenses?
Most people can wear contact lenses, but some may require specialized lenses due to eye conditions.
Good Candidates for Contacts
- People with mild to moderate refractive errors – Contacts work well for nearsightedness, farsightedness, and astigmatism.
- Active individuals – Great for sports and those who prefer a glasses-free look.
- People comfortable with eye handling – Contact lenses require insertion, removal, and proper hygiene.
Who Might Struggle with Contacts?
- Individuals with dry eye syndrome – Some people may find contacts uncomfortable due to low tear production.
- Severe astigmatism or keratoconus patients – May need scleral lenses or other specialty contacts.
- People with allergies or frequent infections – Contact lenses may increase irritation.
Not sure if contacts are right for you? A comprehensive eye exam can help determine the best option.
How Often Should You Update Your Prescription?
Both contact lens and glasses prescriptions should be updated regularly to ensure optimal vision and eye health.
- Contact lens prescriptions are valid for one year in most states.
- Glasses prescriptions typically last one to two years, depending on state regulations.
Annual eye exams help ensure your prescription stays up to date and your eyes remain healthy.
Making an Informed Decision
Contact lens and glasses prescriptions are not the same because they require different measurements and specifications. If you want to switch to contact lenses, a proper fitting and prescription are essential for comfort and clear vision.
Schedule Your Contact Lens Exam at Moses Eyecare Center
At Moses Eyecare Center, we’re focused on your eye health. Our team offers comprehensive eye exams, contact lens fittings, and personalized care at multiple locations across Indiana.
Whether you’re new to contact lenses or need an updated prescription, we’re here to help you see your best.
Schedule an appointment today to find the best contact lens solution for your vision needs.
