How to Read Your Contact Lens Prescription
Contact lenses are your golden ticket to clear vision and freedom from glasses. Let's break down what makes up your prescription.
Sample contact lens prescription
Here's what those abbreviations mean:
- OD: Oculus dexter, the Latin term for right eye
- OS: Oculus sinister, the Latin term for left eye
- OU: Oculus uterque, the Latin term for left eye
- SPH: Sphere (also referred to as Power or PWR)
- BC: Base Curve (usually a number between 8 and 10)
- If your brand only comes in one base curve, your prescription will not contain a BC value
- Like clothing, just because you're a BC 8.6 in one brand doesn't mean you'll be the same in another brand
- DIA: Diameter (usually a number between 13 and 15)
- Brand: The contact lens brand your doctor fitted for your eyes
Astigmatism-correcting lensesPrescriptions to correct astigmatism contain two additional numbers that are usually separated by an "X" and indicated by the following abbreviations:
- CYL: Cylinder (usually a number between -4.00 and +4.00)
- AX: Axis (usually a number between 0 and 180)
Bifocal or MultifocalBifocal or multifocal lens (in one or both eyes) prescriptions contain an additional number with the following abbreviation:
- ADD: Also known as "Add Power" or "Extra Strength"
Why your contact lens prescription is important
Unlike glasses that sit about 12 mm from your eyes, contact lenses sit on your eyes—making the two prescriptions very important and very different. And because we’re sticklers for healthy vision, we can’t process your contact lens order without one.
Contact lens exams measure your eye surface so that doctors can prescribe a contact fitted for your exact eye shape. The prescription may also include how often your contacts should be replaced (monthly, bi-weekly, weekly, daily) to avoid eye damage through infections caused by the buildup of protein, calcium, lipids and other substances found in your tears. And while this isn’t as common, you may have a regular prescription for one eye and a toric (astigmatism) or bifocal prescription for the other. In this case, you’ll have different parameters for each eye and usually a different brand or type of lens as well.
Contact lens prescriptions are typically good for one year and contain information specific to you and your eyes. So, before ordering, make sure you have a valid prescription from your doctor to ensure the health of your eyes.