The short answer is no, a contact lens prescription is not the same as a glasses prescription, even though both correct your vision. While they both aim to achieve the same result – clear vision – the way they achieve it and the measurements involved differ significantly. This is because contact lenses sit directly on the cornea, while glasses sit a distance away from the eye. This difference in position requires different measurements and calculations.
Let's delve into the specifics:
Why Are Contact Lens and Glasses Prescriptions Different?
The key difference lies in the vertex distance. This is the distance between the front surface of the eye and the corrective lens (either glasses or contact lenses). Glasses have a significant vertex distance, typically around 12-14mm. Contact lenses, however, have virtually zero vertex distance because they rest directly on the cornea.
This seemingly small difference drastically affects the refractive power needed to correct your vision. The calculation of this refractive power is complex and takes into account the vertex distance. A prescription that works perfectly for glasses won't necessarily provide the same clear vision when used for contact lenses, and vice versa.
What Are the Differences in Measurements?
While both prescriptions will include a sphere (SPH), cylinder (CYL), and axis (AX) for astigmatism correction, and an add for near vision (if needed for reading), the actual numbers will differ. The key difference is in the power (SPH and CYL) prescribed. The power in a contact lens prescription accounts for the lack of vertex distance, requiring adjustments to achieve optimal clarity. An optometrist or ophthalmologist uses specialized formulas and equipment to make these calculations.
What Happens If I Use the Wrong Prescription?
Using a glasses prescription for contact lenses or vice versa can lead to several issues:
- Blurred Vision: The most common problem is simply blurry or unclear vision.
- Eye Strain: Your eyes will have to work harder to compensate for the incorrect correction, leading to fatigue and discomfort.
- Headaches: Prolonged eye strain can cause headaches.
- Eye Irritation: Incorrect lens placement or power can cause irritation and discomfort.
Can I Use My Glasses Prescription to Order Contact Lenses Online?
Absolutely not. Attempting to order contact lenses using your glasses prescription can be detrimental to your eye health. It's crucial to obtain a contact lens prescription from an eye care professional. They will perform a thorough eye exam specifically for contact lens fitting, determining the correct parameters for your eyes and the type of contact lens best suited for you.
What About Disposable Contact Lenses vs. Traditional Contact Lenses?
While the principle remains the same – the prescription needs to be specific to the contact lens type – the material and type of contact lens further influence the prescription calculation. Disposable contact lenses, for example, might have different parameters compared to traditional reusable contact lenses.
How Often Should I Get My Eyes Checked?
Even if you're using the same type of contact lenses, regular eye exams are crucial. Your prescription can change over time due to various factors, and regular checkups ensure you're using the correct prescription for optimal vision and eye health. Your eye doctor will advise on the recommended frequency, typically annually or as needed.
In conclusion, while both glasses and contact lenses correct vision, their prescriptions are distinct and require different measurements due to the varying distances between the corrective lens and the eye. Always consult an eye care professional for accurate prescriptions for both glasses and contact lenses. Never attempt to self-prescribe or use one type of prescription for the other.
