Key Takeaways
- Glasses and contact lens prescriptions are not the same and cannot be swapped.
- Contacts sit directly on your eye, so their power values can differ from those of your glasses prescription.
- A contact lens prescription includes extra measurements like base curve and diameter.
- A separate contact lens exam and fitting is needed to get your contact lens prescription.
Contact Lenses & Glasses Need Different Prescriptions
You finally got your eyes checked, and now your optometrist is handing you a prescription. You’re thinking about trying contact lenses, so you pull out that slip of paper and wonder if you can just use it to order a pair. It seems like it should work, right?
Glasses and contact lens prescriptions are not the same, and using one in place of the other can affect your comfort and how clearly you see. At Dr. Rehana Manji and Associates, we can help you sort through the details with a proper contact lens exam and fitting.
Why Your Two Prescriptions Are Different
The gap between your glasses and your eye might seem small, but it’s still important. Glasses sit about 12 millimetres away from your cornea, while contact lenses sit directly on it. That difference in position changes how light bends as it enters your eye and means that your glasses prescription could cause blurry vision if applied to your contacts.
If you’re curious about how prescriptions fit into a visit to your optometrist, here’s what to expect during a comprehensive eye exam.
What’s on a Glasses Prescription
Your glasses prescription covers the optical power your lenses need to correct your vision at a 12-millimetre distance. You’ll typically see a few key values on the page.
- Sphere (SPH): the amount of lens power needed to correct nearsightedness or farsightedness
- Cylinder (CYL) and axis: corrects for astigmatism, which affects how light focuses on your retina
- Add (ADD): an additional power value for multifocal lenses, used when reading or close-up vision needs support
These numbers tell the lab exactly how to shape your lenses, but they don’t include everything a contact lens needs. If you’re looking for frames or lens options once you have your prescription, our eyewear collection at Dr. Rehana Manji and Associates includes a range of styles and lens types to suit different visual needs.
What’s on a Contact Lens Prescription
Measurements Unique to Contacts
Because a contact lens sits on your eye, it needs to fit the actual shape of your cornea. Your contact lens prescription includes measurements that have nothing to do with your glasses.
- Base curve (BC): matches the curvature of your eye so the lens sits comfortably and stays in place
- Diameter (DIA): determines how much of your eye the lens covers
- Lens type or brand: specified based on your eye health, tear film, and day-to-day lifestyle
A lens that doesn’t fit your cornea’s curve can feel uncomfortable, move around, or affect your vision, even if the power is correct.
Why Power Values Can Differ
The sphere power on your contact lens prescription may be slightly different from the one on your glasses prescription. This difference accounts for the change in lens position. For lower prescriptions, the difference is often small. For stronger prescriptions, it can be more noticeable.
Cylinder and axis values are only included on a contact lens prescription if you have astigmatism that needs correction. Not every contact lens prescription includes these numbers.
Types of Contact Lenses to Know About
Soft and Daily Lenses
Soft lenses are a common choice for a reason. They tend to feel comfortable quickly and come in daily or monthly options. If you have an active lifestyle or just want the flexibility of not cleaning lenses every night, daily disposables can be a practical fit. For a broader look at the different types of contact lenses available, the CDC provides a helpful breakdown of soft versus hard materials and wear schedules.
Specialty Lenses
Not every prescription fits a standard soft lens. Depending on your eyes, an optometrist in Liberty Village may recommend specialty contacts.
- Toric lenses: designed to correct astigmatism with consistent lens positioning on the eye
- Multifocal lenses: address presbyopia, the gradual shift in near vision that often starts in your 40s
- Scleral lenses: cover a larger surface area and can help those with dry eye or irregular cornea shape
What a Contact Lens Exam and Fitting Includes
Your regular eye exam gives you a glasses prescription. A contact lens fitting is a separate appointment that sets you up to wear contacts. This includes:
- Corneal curvature measurement to find a lens shape that fits your eye properly
- Tear film and overall eye health evaluation to check if contacts are a comfortable option for you
- Trial lenses so you can assess real-world comfort, vision, and fit before committing to a full supply
If you’re curious about contact lenses or want to understand your prescription better, our team at Dr. Rehana Manji and Associates can walk you through the process. As an optometrist in Liberty Village, we take the time to listen to your needs and help you find a lens option that fits your eyes and your lifestyle. Reach out to book your contact lens fitting today.
