How to Convert Eyeglass Prescription to Contact Lens Prescription
Eyeglass Prescription vs. Contact Lens Prescription
Understanding the difference between an eyeglass prescription and a contact lens prescription is important before ordering contact lenses online. Although both prescriptions correct vision, they are not always interchangeable.
At KPOP2, we recommend using a current, valid contact lens prescription when ordering prescription contact lenses. If you only have an eyeglass prescription, consult an eye care professional before selecting your contact lens power.
Why Are Eyeglass and Contact Lens Prescriptions Different?
Eyeglasses are positioned in front of the eyes, while contact lenses sit directly on the surface of the eye. Because the optical position is different, the required lens power can also differ, particularly with stronger prescriptions.
For lower prescriptions, the numerical power may sometimes be the same for glasses and contact lenses. However, this should not be assumed for every wearer. Higher prescriptions may require a vertex-distance adjustment, and the final contact lens prescription should be determined by an eye care professional.
Important: An eyeglass prescription should not be treated as a substitute for a contact lens prescription. Contact lenses require a prescription appropriate for the specific lens and your eyes.
When Can the Power Be Different?
The difference becomes more relevant as prescription strength increases. This is related to the distance between the corrective lens and the eye, known as vertex distance.
For example, a person with a stronger minus eyeglass prescription may require a slightly different contact lens power. However, there is no single conversion rule that should be applied to every wearer.
Rather than automatically converting your glasses prescription, an eye care professional can determine the appropriate contact lens power and evaluate whether the selected lens is suitable for your eyes.
Why You Should Not Convert Your Prescription Yourself
A contact lens prescription contains more information than sphere power alone. Depending on the lens, it may include:
- Sphere (SPH) or prescription power
- Cylinder (CYL) and axis for astigmatism correction
- Base curve (BC)
- Diameter (DIA)
- Brand or specific lens information, when applicable
- Prescription expiration date and other prescribing information
Colored contact lenses can also differ in material, water content, design, diameter and replacement schedule. A prescription that is appropriate for one contact lens may not automatically be appropriate for another.
Example: Why a Simple Conversion Table Can Be Misleading
| Eyeglass Prescription | Contact Lens Power | What to Do |
|---|---|---|
| -1.00 | May be similar | Use your contact lens prescription |
| -4.00 | May differ | Do not assume the same power |
| -5.00 | May require adjustment | Consult an eye care professional |
| -6.00 | May require adjustment | Consult an eye care professional |
These examples are for general explanation only and are not a prescription conversion chart. The correct contact lens power must be determined from your contact lens prescription.
What If I Only Have a Glasses Prescription?
If you have a glasses prescription but do not have a contact lens prescription, the safest approach is to have your eyes evaluated and obtain a current contact lens prescription before ordering.
This is especially important if you are new to contact lenses, have a strong prescription, have astigmatism, or experience discomfort or blurred vision while wearing lenses.
What Information Does KPOP2 Need?
For prescription contact lenses, KPOP2 may need information from your valid contact lens prescription before your order can be dispatched.
A contact lens prescription may include your name, lens power, base curve, diameter, brand or lens specification, expiration date and prescriber information, depending on the prescription and lens type.
If prescription verification is required for your order, please follow the instructions provided by KPOP2 and submit the requested information before dispatch.
Need Help With Your Prescription?
If you are unsure whether your prescription is suitable for a particular lens, please contact KPOP2 before ordering. Our team can help you understand the product information and prescription requirements. For clinical advice or prescription changes, please consult your eye care professional.
Key Takeaway
An eyeglass prescription and a contact lens prescription are related, but they should not automatically be treated as the same prescription. The difference can become more important with stronger prescriptions, and contact lenses also require specifications related to the lens and the wearer's eyes.
For the safest and most accurate selection, use a current contact lens prescription and follow the prescribing guidance provided by your eye care professional.
This information is provided for general educational purposes and is not a substitute for an eye examination, contact lens fitting, or professional medical advice.
