Contact lenses can offer convenience or may just appeal due to their aesthetic. So, if you’re interested in switching from glasses to contact lenses, you may have wondered if you can simply convert the prescription you got for your glasses.
Unfortunately, it’s not so simple. Contact lens prescriptions and eyeglasses prescriptions are different. If you’re interested in contacts, you will need a contact lens exam and fitting to determine specific measurements of your eye.
Everyone’s eyes are different. Visit your optometrist to learn more about contact lenses, how to wear and care for them, and to explore which type of contact lens works for you.
Contact Lens Prescriptions vs. Glasses Prescriptions
The lens in a pair of glasses is approximately 12 millimetres away from the eye. On the other hand, contact lenses lie directly on the eye’s surface. This difference in distance between the lens and eye makes the two prescriptions different. Plus, contact lenses also require additional measurements, like the curvature of the cornea, in order to fit well.
Understanding a Glasses Prescription
If you’ve ever had a glasses prescription, you’ll notice many numbers and abbreviations. Here’s what they mean:
- O.D.: Oculus dexter or right eye
- O.S.: Oculus sinister or left eye
- SPH: The sphere or SPH column of your prescription tells you the lens power needed to correct your vision. Prescription power is measured in diopters: a minus sign conveys a prescription for nearsightedness, while a plus sign conveys a farsightedness prescription.
- CYL: The cylinder or CYL column will be filled if you need correction for astigmatism.
- Axis: This value conveys the location of astigmatism on the cornea.
- Add: This column may be filled if you require additional lens powers, such as in the case of bifocals.
- Prism: This section will be filled for people who need correction for double vision.
Understanding a Contact Lens Prescription
Because contact lenses sit directly on the eye, their prescription power may be different. Contact lens prescriptions also include other values, including:
- Base curve: This value is essential for fitting the lens against the curvature of your eye. It’s a number between 8 and 10.
- Diameter: This is the width of the contact lens, typically 13 to 15 millimeters.
- Brand and type: Contact lenses vary in their degree of oxygen permeability, so lens type and brand are required for a valid prescription.
- Expiration date: A contact lens prescription is typically valid for one year. Be sure to get an annual contact lens exam to check how your lenses fit.
What to Expect During a Contact Lens Exam & Fitting
During a contact lens exam and fitting, an optometrist gathers information to create a personalized prescription based on a patient’s vision needs and eye measurements. The optometrist will also take into account the patient’s eye health and lifestyle when choosing a type of contact lens.
Here’s what you can expect during a contact lens exam and fitting:
- Getting to know you: Your optometrist may ask about your work and recreational habits in order to better understand your visual needs. This can inform the type of lens they recommend. They may also ask about your medical history, as contact lenses aren’t suitable for everyone.
- Refraction test: Your optometrist will assess how well you see to determine the correct prescription power. This is often done by reading letters using a variety of lens powers with a device called a phoropter.
- Eye measurements: Your optometrist will measure parts of your eyes, including the curvature of your cornea, the size of your pupils, and sometimes, your irises.
- Tear film health assessment: Sometimes, people with dry eye disease struggle to wear contact lenses. Your optometrist will assess the health of your tear film, which is a layer of lubricating fluid on your eye’s surface.
- Trial lenses: At our clinic, we’ll also test different lenses to see how they fit on your eyes.
A contact lens exam is also your opportunity to ask your optometrist about how to wear and care for your lenses. We suggest scheduling follow-up appointments to check up on how you’re adjusting to your contacts.
More About Contact Lenses
There are many different types of contact lenses. Contacts are often described by their material, wear schedule, and replacement schedule. Our clinic offers:
- Soft contact lenses: Made of pliable plastic, many people find these contacts comfortable to wear. However, they’re more prone to collecting irritants and are more fragile.
- Rigid gas-permeable lenses: These contact lenses are harder, but they’re designed to allow oxygen to flow through. RGP lenses can be less comfortable than soft ones, but many people find they produce crisper vision.
- Scleral lenses: This type of RGP lens lies on the sclera (the white part of your eye) rather than the cornea. They have a space between the cornea and the lens that holds fluid, and are often used for people with dry eye disease or diseases of the cornea.
- Contact lenses for myopia control: Some contact lenses are designed to slow the progression of myopia (nearsightedness) in children.
Get Fitted With Contacts in Petaluma
When it comes to prescription eyewear, you have numerous options to help you see clearly. Some people prefer the convenience and aesthetic of contact lenses, while others enjoy the simplicity of eyeglasses. Understanding your prescription can be complex, so don’t hesitate to reach out to us if you have any questions. At Bright Eyes Optometry, our mission is to develop lifelong relationships with each of our patients. To schedule an eye exam or contact lens fitting, contact us today.
