You may think that if you have a prescription for glasses, you can simply use those same numbers to buy contact lenses. At Bonavista Eyecare, Olds Eyecare, Sundre Eyecare and Carstairs Eyecare this is a common point of confusion for people who want to try contact lenses for the first time. It seems logical: After all, both are meant to help you see clearly.
The simple answer is no, your prescription for contact lenses is not the same as your prescription for glasses. Each prescription contains unique measurements designed to show how the lens corrects your vision at a specific distance.
Why Your Prescriptions Are Different
How Lenses Sit on Your Eye
Think about where your glasses rest. They sit on your nose, about 10–14 millimetres away from your eyes. This small distance makes a big difference in how vision-correcting glasses need to bend light to help you focus.
Contact lenses, on the other hand, sit directly on the surface of your eye. Because there is no gap, the power of the lens must be adjusted. A prescription is calculated with this placement in mind to give you clear vision.
Power Conversion and Calculation
The numbers on your glasses prescription are not a direct match for a contact lens prescription. An eye care professional may use your glasses prescription as a starting point and then perform a calculation to convert the power.
This adjustment accounts for the change in distance from your eye to the lens. The final numbers on your contact lens prescription will look different because the strength is specific to a lens that rests on your eye’s surface.
What a Glasses Prescription Includes
Your prescription for glasses contains a few key pieces of information to correct your vision. You might notice abbreviations for different measurements, each with a specific role.
- Sphere (SPH): This number corrects for nearsightedness or farsightedness.
- Cylinder (CYL) and axis: These measurements correct for astigmatism, which is an imperfection in your eye’s curve.
- Add: This is the extra power added to bifocal or multifocal lenses for reading.
Extra Details for a Contact Lens Prescription
Base Curve and Diameter
A contact lens prescription also includes measurements that are all about a proper fit. The base curve (BC) number matches the curvature of your cornea (the clear front part of your eye). The diameter (DIA) measurement determines the width of the lens.
Getting these 2 measurements right helps the lens sit comfortably and safely on your eye. An improper fit can feel uncomfortable or even affect your eye health, so these details are important for safe contact lens wear.
Lens Brand and Material
Your prescription can also name a specific brand and type of contact lens. Different lenses are made from different materials, which affect how much oxygen and moisture reach your eye.
An eye doctor at any 1 of our 4 locations can recommend a specific type of lens from a particular contact lens brand based on your eye health, lifestyle, and visual needs. This helps your eyes stay comfortable throughout the day.
Common Questions About Your Vision
Why Is My Vision Blurry with Contacts?
When you first wear contacts, your vision might seem a little off. Sometimes, your eyes just need a few days to get used to them. Blurriness can also happen if the fit needs a small adjustment.
Can I Wear Contacts with Dry Eye?
Wearing contacts with dry eye can sometimes make your vision a little blurry, as contacts can disrupt your tear film. The good news is that there are contact lenses designed for dry eye that can help. If your vision with contacts is not as clear as you expect, it’s a good idea to mention it to your eye doctor during a follow-up appointment.
Get the Right Fit for Your Eyes
A Contact Lens Exam
A contact lens exam is different from a regular eye exam. It includes precise measurements of your eye’s surface to determine the correct lens size and shape. Your eye health is also checked to see if you are a good candidate for wearing contacts.
This exam usually includes a trial pair of lenses. This lets you see how they feel and function before you commit to a full supply.
Your Next Step for Clear Vision
To get the right fit, schedule a contact lens fitting. This dedicated appointment helps confirm that all the unique measurements for your eyes are taken correctly. You can discuss your options with an eye doctor to find a comfortable solution.
Schedule Your Contact Lens Exam Today
Our team can help guide you through the process across any of our 4 locations. Having a separate, accurate prescription for your contacts is key to seeing clearly and comfortably. For a personal and unhurried experience, schedule your contact lens exam today.
