You might look at your glasses prescription and wonder if you can use it to order contact lenses online. After all, since they both help you see clearly, the numbers should be the same, right?
In fact, prescriptions for glasses and contact lenses aren’t the same and can’t be used interchangeably. This is because they use different measurements to give you clear and comfortable vision.
If you want to wear contacts, you’ll need to schedule a contact lens fitting with our team at Perspectives Vision Clinic.
Why Your Two Prescriptions Are Not Interchangeable
The main reason for the difference comes down to the distance that each corrective device sits from your eye. Your glasses rest in front of your eyes, usually about 12 millimeters away. This space might not seem like much, but it changes how light travels through the lens to reach your retina. Contact lenses, on the other hand, sit directly on the surface of your eye.
This space between your glasses and your corrective device is called the vertex distance. Your eye doctor accounts for vertex distance when determining the right lens power for your glasses. For contact lenses, this value is zero, so lens power has to be adjusted accordingly.
For people with a mild prescription, the difference between their prescriptions might be small. However, for those with worsening eyesight or a stronger prescription, the difference in power between your glasses and contacts can be more significant.
Contacts Require Extra Measurements
A contact lens prescription includes details that have nothing to do with your vision and everything to do with the physical fit. These measurements, determined during a contact lens fitting, help make your new lenses comfortable and safe for your eyes.
- Base Curve: This measures the curvature of the contact lens, so it matches the shape of your cornea.
- Diameter: This determines the overall width of the lens to make sure it covers your cornea properly.
These details help your optometrist select the right material and type of contact lens.
What Each Prescription Includes
A prescription for glasses is quite different from one for contacts. In fact, you cannot legally or safely purchase contact lenses using only your glasses prescription.
- A glasses prescription contains values for sphere, cylinder, and axis to correct refractive errors.
- A contact lens prescription also contains values sphere, cylinder, and axis, but also includes the lens brand, base curve, and diameter of your lenses.
The Importance of Separate Eye Exams
Getting fitted for contacts requires more than a standard eye exam. A contact lens fitting helps check that the lenses you choose are a healthy match for your eyes. During the fitting, your eye doctor will check the movement and positioning of your lenses and offer guidance on proper contact lens care to prevent potential discomfort.
If you’re interested in trying contact lenses or need an updated prescription, our team at Perspectives Vision Clinic is ready to help. Schedule your contact lens exam to get a precise fitting and discover the freedom of clear vision without glasses.
