What to Know About Contact Lens Prescriptions

If you have worn eyeglasses before, your contact lens prescription may be slightly different. Here’s why.

Woman wearing contact lenses

If you wear contact lenses, you will have a contact lens prescription that you get from your eye doctor.

Here are some tips to understand it:

  • If you have worn eyeglasses before, your contact lens prescription may be slightly different. This is because eyeglasses are further from the eye and contact lenses sit directly on the eye.

  • Always get a copy of your prescription. You are entitled to a copy of your contact lens prescription by law. Do research and ask your eye doctor questions so that you understand it completely. If you are confused or have questions, make sure to get clarifications. Depending on your state's laws, prescriptions for contact lenses last 1-2 years. Once your prescription has expired, you must get a new one. It may seem like a pain, but it is in the best interest of your eye health to ensure proper prescriptions for your contact lenses.

  • There are many terms, abbreviations and measurements shown on your contact lens prescription. Specific terms must be placed on the label in order to follow appropriate laws.

Did you know that contact lens prescriptions need to be renewed every year? Click here to find an exam time that fits your schedule. 

Here are the common things you will see on the prescription:


OS (ocular sinister) is Latin for the left eye. OD (ocular dexter) is Latin for the right eye. If you have OU (means ocular uterque), then the prescription is the same measurement in both eyes.


This stands for base curve. It is the back curvature of your contact lens measured in millimeters. Your prescription will match the curvature of your cornea for the ideal fit and health of your eye. The lower the number, the steeper the curve is in your cornea.


This stands for the diameter. It's the distance from one edge of your contact lens to the other. This is also measured in millimeters. It determines where the edges of the lens will rest on your eye. A correct measurement here reduces irritation from a contact lens.


This stands for add power and is used with bifocal lenses. The add power is measured in diopters.

America's Best's Owl
What’s popular right now? Savings.

Two pairs and a free, quality eye exam for just $79.95


This is included in the prescription only if the lenses change or enhance the color of your eyes. In the case of a special effect, a particular design is written here. Color and style names vary by brand.


This is the manufacturer's name of the contact lens. If you have astigmatism, these CYL and AXIS will also appear on your contact lens prescription.


This stands for cylinder. Measured in diopters, the cylinder shows the extent of your astigmatism. A negative sign means nearsightedness and a plus sign means farsightedness.


This isn't short for anything as it just refers to the axis. The axis is measured in degrees and indicates the orientation of the cylinder in the lens. It is used in order to compensate for the oval shape of the cornea.

Remember to always consult your eye doctor with any specific questions you have about your contact lens prescription.

Recommended reading: America's Best Guide to Contact Lenses