Understanding your contact lens prescription helps you order correctly and wear safely. Read this guide carefully before placing an order.
Medical Disclaimer: This guide is for informational purposes only. It does not constitute medical advice. Always consult a licensed eye care professional (ophthalmologist or optometrist) for a proper eye examination and prescription. PrimeLens Nepal is not responsible for any vision problems resulting from self-diagnosis or self-prescribed parameters.
Reading Your Prescription
A contact lens prescription is different from a glasses prescription. Ensure you have a contact lens prescription — not just a spectacle prescription — before ordering. A contact lens prescription includes parameters specific to contact lenses and is only valid after a proper contact lens fitting.
Key Parameters Explained
OD / OS
OD = Right eye (oculus dexter)
OS = Left eye (oculus sinister). Always order separately for each eye if they differ.
Power (PWR / SPH)
Your corrective power in diopters. Negative (–) for myopia (short-sightedness); positive (+) for hyperopia (long-sightedness).
Base Curve (BC)
The curvature of the lens back surface, in mm. Typically 8.3–9.0. Must match your eye’s curvature for comfort and safety.
Diameter (DIA)
The total width of the lens in mm. Typically 13.8–14.5 for standard lenses, 14.0–16.0 for colour lenses. Affects how the lens fits on your eye.
Cylinder (CYL)
Only for astigmatism correction. Always negative. Toric lenses have a CYL value; if your prescription has no CYL, you do not need toric lenses.
Axis
Paired with CYL for astigmatism. A number from 1–180 indicating the orientation of astigmatism correction. Required for toric lenses.
Sample Prescription
| Eye | Power | Base Curve | Diameter | Cylinder | Axis |
|---|---|---|---|---|---|
| OD (Right) | –2.50 | 8.6 | 14.2 | – | – |
| OS (Left) | –1.75 | 8.6 | 14.2 | –0.75 | 180 |
In this example, the right eye is a standard spherical lens. The left eye requires a toric lens (astigmatism) with a cylinder of –0.75 at axis 180.
Prescription Validity
Contact lens prescriptions in Nepal are typically valid for 1–2 years from the date of your last eye examination, at the discretion of your prescribing doctor. PrimeLens Nepal strongly recommends annual eye check-ups. Wearing an expired prescription can result in inadequate vision correction and potential harm to your eyes.
Prescription for Colour Lenses (Plano / Zero Power)
Even if you have perfect vision and want colour lenses for cosmetic purposes (plano/0.00 power), you still need a contact lens fitting from an eye care professional. The fitting ensures the base curve and diameter are appropriate for your eyes. PrimeLens Nepal strongly advises against purchasing colour lenses without professional guidance.
Toric & Multifocal Lenses
If you are trying toric (astigmatism) or multifocal lenses for the first time, a mandatory trial lens fitting is required with your eye care provider before purchasing. For any complaints or return requests, we will require your previous purchase record showing successful use of the same lens parameters.
Common Ordering Mistakes to Avoid
- Ordering contact lens parameters from a glasses prescription (they are not the same).
- Entering power as positive when it should be negative or vice versa.
- Ordering the same base curve for both eyes when they differ.
- Ignoring the cylinder/axis values for astigmatic eyes.
- Ordering a higher replacement frequency lens than prescribed (e.g., using a monthly lens as a yearly lens).