When you’re running low on your contact lens supply or your glasses need an update, your optometrist is the one to turn to. Although both tools can comfortably correct your vision, they interact differently with your eyes, a detail that is reflected in your final prescription.
No, contact lenses and glasses do not share the same prescription and are not interchangeable. Swapping one for the other can affect the quality of your vision, eye health, and overall comfort.
With annual contact lens exams, you get the best of both: an updated contact lens and glasses prescription. It’s all about what works perfectly for you!
The Details of Your Glasses Prescription
A final glasses prescription marks the end of most people’s routine eye exam. But not everyone knows what these numbers mean.
From left to right, here’s what a typical glasses prescription includes:
- Sphere (SPH): This measures the lens power needed to correct nearsightedness or farsightedness. A negative number indicates nearsightedness (myopia), while a positive number indicates farsightedness (hyperopia).
- Cylinder (CYL): This corrects astigmatism, which occurs when your cornea has an irregular shape. Not everyone has astigmatism, so this field might be blank on your prescription.
- Axis: If you have astigmatism, this number (between 1 and 180) indicates the orientation of your astigmatism correction on the physical glasses lens.
- Add Power: For those who need multifocal lenses, this indicates the additional magnifying power needed for close-up work.
Reading Your Contact Lens Prescription
A contact lens prescription includes some of the same baseline information as one for glasses, along with some added details:
- Base curve (BC): This measurement determines how the contact lens curves to match the shape of your eye. The wrong base curve can cause discomfort, poor vision, or even eye damage.
- Diameter (DIA): This measures the width of the contact lens from edge to edge. The diameter affects how the lens centers on your eye and how much of your cornea it covers.
- Brand and material: Contact lenses are made from specific materials that affect comfort, oxygen permeability, and wear time. Your prescription will specify the exact brand and type recommended.
Contacts vs Glasses Prescription: Why Distance Matters
Corrective lenses have one goal: to provide clear, sharp vision. However, contact lenses and eyeglasses achieve it differently.
Contacts are lenses that sit on the corneal surface, constantly interacting with your eyes. This allows a more natural field of vision, without glasses’ frames obstructing your view or sliding down your nose.
Meanwhile, glasses are much more noticeable, rest comfortably on the bridge of your nose (about 12 millimeters away from your eyes), and require much less maintenance. Though this gap might seem insignificant, it affects how light enters your eyes, and naturally, the power (or strength) of the lens.
Are These Prescriptions Interchangeable?
Many people assume they can take their glasses prescription to order their contacts online. There might be subtle differences in the lens powers, but how bad can it be? The reality is that this can lead to several problems:
- Comfort issues: An incorrect base curve or diameter measurements (remember, glasses prescriptions don’t need them) can lead to lenses that don’t fit properly. This might cause irritation, excessive lens movement, or the feeling that something is constantly in your eye.
- Poor vision correction: Incorrect power calculations can result in blurry vision or eye strain. You might find yourself squinting more or experiencing headaches.
- Eye health concerns: Poorly fitting contacts can restrict oxygen flow to your eyes or cause scratches on the corneal surface. Over time, this could lead to more serious complications.
An annual contact lens exam and fitting prevent these concerns from happening altogether. Even if your vision seems fine, your prescription might need updating, or your eye health status could change.
Your Guide to a Contact Lens Fitting
A proper contact lens prescription requires more than converting the numbers of your glasses prescription. Here’s what you can expect during your contact lens fitting:
- Eye health evaluation: Even if you’ve been wearing contacts for years, we always evaluate the health of your eyes to verify that they can safely sustain lens use. This helps us determine if you benefit from switching to a different lens type, like daily disposables or a specialty lens.
- Measuring your eye shape: The shape and size of your eyes influence your contact lens prescription. The lens itself should fit snugly—not too tight or too loose. Measuring the curve and size of your eyes helps determine the right base curve and diameter.
- Contact lens education: If you’re new to contact lenses, we’ll teach you how to safely insert, remove, and care for your contact lenses.
- Trial fitting: You’ll typically try on sample lenses to confirm proper fit, comfort, and vision quality. This step helps identify any adjustments needed before finalizing your prescription.
- Follow-up care: After the trial period is over, we schedule a follow-up appointment for one final check-in. If everything looks and feels great, we can finalize your contact lens prescription! If not, that’s okay. This trial period allows us to address any concerns.
If you’re looking to replenish your contact lenses, a valid contact lens prescription is a must. Yes, they expire annually, but it encourages people to stay on top of their routine eye exams.
Invest In Your Vision
Glasses and contact lenses share some similarities, but prescriptions are not one of them.
Contacts are popular for a reason. They offer a more natural field of vision, and with the right prescription, you might not even realize you’re wearing them! While the perks are great, remember that contacts require proper care and handling, which includes staying on top of your annual contact lens exam and fitting. If you’re looking to replenish your contact lens supply or try contacts for the first time, a contact lens exam and fitting is what you need. Connect with our Pine Creek Vision Clinic team to book your appointment.
