Your contact lens prescription looks like a row of short codes. Each one describes a different part of the lens your eye doctor chose for you. This guide explains what they mean so you can check your lenses before you order. It does not replace your eye doctor's advice: always order exactly what your prescription says.
Contact lens and glasses prescriptions are different
A glasses prescription cannot be used to order contact lenses. Glasses sit about 12 mm from your eyes, while contact lenses sit directly on them, so the power can differ. A contact lens prescription also includes the lens brand and measurements of the lens fit, which a glasses prescription does not have. Your eye doctor takes these during a contact lens fitting.
OD and OS: right eye and left eye
OD is your right eye and OS is your left eye. Some prescriptions use R and L instead. Your two eyes often have different values, so check each line separately. (On ContactLensDirect, choose the eye option for each lens when you order.)
Brand
Your prescription names a specific lens brand and product, for example a daily or monthly lens from a particular maker. Lenses from different brands can differ in material, shape and replacement schedule, so a similar-looking lens is not the same lens. If you want to change brand, ask your eye doctor first; they may need to update your prescription.
Power (PWR or SPH)
Power is measured in diopters (D) and shows how strongly the lens corrects your vision.
- A minus (−) number means nearsightedness (myopia): distance is blurry.
- A plus (+) number means farsightedness (hyperopia): near vision is often harder.
- The further the number is from zero, the stronger the correction.
Cylinder (CYL) and axis: for astigmatism
These two numbers appear only if you have astigmatism and need a toric lens.
- Cylinder (CYL) is the extra power that corrects astigmatism, usually written as a minus number.
- Axis is a number from 1 to 180 degrees that tells the lens how to sit on your eye, because a toric lens must stay in the right position.
Both must be entered exactly as written when you order. Browse toric lenses for astigmatism once you have your values.
Add (ADD): for multifocal lenses
If you wear multifocal lenses for presbyopia, your prescription has an ADD value. This is extra power for near vision, shown as a plus number or sometimes as a letter or word such as Low, Mid or High, depending on the brand. Some multifocal prescriptions also mark which eye is dominant (D) and which is non-dominant (N).
Base curve (BC)
Base curve is the curvature of the back of the lens, in millimeters. It describes how the lens fits the front of your eye. A lower number means a steeper curve and a higher number a flatter one. Most soft lenses sit between roughly 8 and 9 mm. Do not change the base curve on your own.
Diameter (DIA)
Diameter is the width of the lens in millimeters. It affects how much of your eye the lens covers and how it sits. Soft lenses are usually a little over 14 mm wide.
Expiry date and your copy
Your prescription has an issue date and an expiry date. Under the US Contact Lens Rule, a prescription lasts at least one year unless your eye doctor sets a shorter period for a documented medical reason, and state law may allow longer. Your eye doctor must give you a copy after your fitting. Sellers may verify your prescription with your eye doctor before sending lenses, and if the doctor does not respond within eight business hours, the prescription is treated as verified.
Example
| Brand | Power | Cyl | Axis | BC | DIA | |
|---|---|---|---|---|---|---|
| OD (right) | Example lens | −2.50 | −1.25 | 180 | 8.5 | 14.3 |
| OS (left) | Example lens | −2.25 | −0.75 | 170 | 8.5 | 14.3 |
(Example values for illustration only. Do not use them to order.)
Before you order
- Check that the brand and product match what you are ordering.
- Match every value for each eye exactly: power, cylinder, axis, add, base curve and diameter, where they appear.
- Check the expiry date.
- If anything is unclear, ask your eye doctor's office.
You can then browse our daily, 2-week and monthly lenses.
This article is for information only and is not medical advice. Always follow your eye care professional's guidance and the prescription they gave you.
