How to Read a Contact Lens Prescription

What Is a Contact Lens Prescription?

A contact lens prescription is a written order from your eye doctor that specifies the exact parameters needed for your lenses to correct your vision safely and comfortably. It is different from an eyeglass prescription — contact lens prescriptions include additional measurements specific to the lens sitting directly on your eye.

Your prescription is typically valid for 1–2 years, depending on your state and your eye doctor's recommendation. Always use a current, valid prescription when ordering lenses. Browse our full range of All Lenses to find the right fit for your prescription.

Breaking Down the Abbreviations

OD and OS

These are Latin abbreviations for your two eyes:

OD (Oculus Dexter) — your right eye
OS (Oculus Sinister) — your left eye

Some prescriptions also use OU (Oculus Uterque), meaning both eyes together.

PWR / SPH (Power / Sphere)

This is the lens power needed to correct your vision, measured in diopters (D). It will be a positive (+) or negative (−) number:

Negative numbers (e.g., −2.50) correct nearsightedness (myopia)
Positive numbers (e.g., +1.75) correct farsightedness (hyperopia)

BC (Base Curve)

The base curve describes the curvature of the back surface of the lens, measured in millimeters (e.g., 8.4 or 8.6). It determines how the lens fits on your eye. Using the wrong base curve can cause discomfort or blurry vision, so always match this number exactly. Popular options like Acuvue lenses come in specific base curves — always verify before ordering.

DIA (Diameter)

Diameter is the width of the lens in millimeters (typically 13.8–14.5 mm for soft lenses). Like base curve, this must match your prescription exactly.

CYL (Cylinder) — for Astigmatism

If you have astigmatism, your prescription will include a CYL value. This is always a negative number and indicates the degree of astigmatism correction needed. If your prescription has a CYL value, you need Toric Lenses designed specifically for Astigmatism.

AXIS — for Astigmatism

The AXIS is a number between 0 and 180 that indicates the orientation of the astigmatism correction. It always appears alongside the CYL value. Both must be matched precisely when ordering Toric Lenses .

ADD — for Presbyopia / Multifocal Lenses

If you need reading correction in addition to distance correction, your prescription may include an ADD value. This is used for multifocal or bifocal contact lenses.

Sample Prescription — What It Looks Like

Eye	PWR	BC	DIA	CYL	AXIS
OD (Right)	−3.00	8.6	14.2	−0.75	180
OS (Left)	−2.50	8.6	14.2	—	—

In this example, the right eye has mild astigmatism (CYL and AXIS values), while the left eye does not.

Can I Use My Glasses Prescription for Contacts?

No. While the power (PWR/SPH) may be similar, a glasses prescription does not include the BC, DIA, CYL, or AXIS values needed for contact lenses. Always get a separate contact lens fitting and prescription from your eye care professional.

Ready to Order?

Once you have your prescription in hand, ordering is straightforward. Browse our collections to find your lenses:

Always consult your eye care professional before changing lens brands or parameters. This article is for informational purposes only and does not constitute medical advice.