You just had an eye exam and have a new prescription for glasses in hand, and it’s tempting to wonder if you can use those same numbers to order a box of contact lenses online. Our team at Envision Eye Care understands why people feel this way, but we want you to understand what makes them different.
No, your contact lens and glasses prescriptions are not the same. They require different information from a contact lens exam because they correct your vision from 2 very different positions. Using a glasses prescription to order contacts can lead to blurry vision or even discomfort.
Why Your Prescriptions Are Different
The Distance From Your Eye
Think about how you wear glasses. They sit a small distance (usually about 12 millimeters) away from your eyes. Contact lenses, on the other hand, rest directly on the surface of your eyes.
This small gap changes the power required to focus light correctly onto the back of your eye (your retina). An eye doctor accounts for this distance when writing each prescription, making sure the power is just right for where the lens will sit.
More Than Just Vision Correction
Contact lenses are considered medical devices because they come into contact with your eye’s surface. A proper fit is about more than just clear vision: It’s about your eye health. A contact lens that doesn’t fit right can affect oxygen flow and lead to irritation, which is why proper care is so important.
What Your Glasses Prescription Shows
Key Numbers for Your Lenses
Your glasses prescription has specific numbers to create the right lenses for your frames. These numbers, determined during a comprehensive eye exam, tell the lens maker exactly how to shape the glass or plastic to correct your vision.
- SPH (sphere): This is the main lens power you need to see clearly, whether you are nearsighted or farsighted.
- CYL (cylinder): This number is for astigmatism, which is when your eye is shaped more like a football than a baseball.
- Axis: If you have astigmatism, the axis tells the lab which way the correction should be on your lens.
The Pupillary Distance Measurement
Your prescription may also include a pupillary distance (PD) measurement. This is simply the distance between the centers of your pupils, or the black part in the center of your eye. This helps the optical center of your lenses line up with your eyes for the clearest view.
What Your Contact Lens Prescription Adds
Base Curve and Diameter
A contact lens prescription includes measurements that your glasses prescription doesn’t. These are needed to match the unique shape of your eye for a clear and comfortable fit.
- BC (base curve): This measures the curvature of the contact lens, which needs to match the curve of your eye.
- DIA (diameter): This number shows the width of the contact lens from edge to edge. It helps the lens cover the right part of your eye.
Lens Brand and Material
Unlike glasses, your contact lens prescription also names a specific brand and type of lens. Different lenses are made from different materials that help varying amounts of oxygen to pass through to your eye. The eye doctor can choose from various contact lens types that might be right for you. Maybe you have dry eye, for example, and need a contact lens designed to help keep your tears comfortable.
The Need for a Professional Contact Lens Fit
Why You Can’t Convert It Yourself
It might seem like you could use an online calculator to convert your prescription, but it’s not that simple. The calculations are complex and require professional knowledge, so going to an eye doctor for help means that you can trust the prescription you’re getting.
What to Expect at a Fitting
During a contact lens fitting, the eye doctor first evaluates your eye health. Then, you can try on trial lenses to check for comfort, fit, and vision. Our team often schedules a follow-up visit to make sure your eyes are adjusting well to the new lenses. We want you to be comfortable, after all.
Make Sure Your Prescriptions Are Current
To help you see clearly, it helps to have prescriptions for both glasses and contacts, especially if you plan to wear both. You can ask our eye doctors in Fort Wayne, Dr. Mummert and Dr. Sadilek, for guidance on what type of exam you need. We want to make sure you get the right care.
Schedule an Eye Exam
Our team at Envision Eye Care is more than just optometrists. We’re your neighbors. Because of that, we have a genuine commitment to helping you understand anything vision-related. Whether you’re looking to try contact lenses for the first time or just needing a fresh prescription, we’d be happy to help. Schedule an appointment today.