How to Read a Contact Prescription

Thinking about switching from glasses to contact lenses? Or are you considering alternating between wearing contacts and glasses?

You may notice that your contact prescription looks different than your prescriptions for glasses. If you're entirely new to receiving prescriptions and you're planning to correct your vision with contacts, the text on the slip of paper may look like a foreign language.

Understanding the abbreviations and numbers may seem complex, but once you know how to read a prescription, you should be able to decipher any contacts prescription that comes your way.

Learn more from the eye care professionals at The EyeDoctors Optometrists about how to read a contact lens prescription.

• Some of the abbreviations that appear in prescriptions are the same, including "OD" for "oculus dexter" and "OS" for "oculus sinister." "OD" is the Latin term for the right eye and "OS" is the term for the left eye.

• Eyeglass prescriptions and contact prescriptions often have the abbreviation "SPH" on them, which stands for "spherical correction." In some cases, they have "PWR" listed instead, which stands for "power." Both terms refer to the strength of the prescription.

  • The number that's listed will be measured in diopters, a term that refers to corrective lens strength. It will be preceded by a plus sign (+) if you're farsighted or a minus sign (-) if you're nearsighted.

• If you have astigmatism — when the cornea, or lens of the eye, has an irregular shape, causing blurry vision — your prescription includes two additional abbreviations. "CYL" is short for "cylindrical power," which determines how strong a cylindrical lens must be to correct your astigmatism. Additionally, the term "Axis" will appear on the prescription, referring to the way that the cylindrical lens needs to be tilted to correct the astigmatism.

  • If you don't need astigmatism correcting lenses, your eye doctor may write "DS," for "diopters sphere," meaning your eyes have a regular, spherical shape.

• Sometimes, an eyeglass or contact prescription may include information labeled "ADD," which is short for "additional correction." This is where details about bifocals, multifocal lenses or progressive lenses would appear.

• Contact prescriptions contain additional numbers and abbreviations that don't appear in eyeglass prescriptions, including "BC," for "base curvature." This refers to the way that your cornea curves. It's necessary to include this detail because the shape of your contact lens needs to correspond to the shape of your cornea to ensure a good fit.

• Contact prescriptions also include the term "DIA," which is short for "diameter," or the distance from one edge of the contact lens to the other. This is measured in millimeters.

• A contact prescription should name the brand of contact lenses that your eye doctor prescribes, as well as an expiration date for the prescription.

• If your eye doctor gives you both prescriptions, you may notice some of the numbers listed alongside the corresponding abbreviations are different. This isn't a mistake; the prescriptions are different because people wear eyeglasses and contacts differently.

  • Contacts sit on the surface of your eye, while eyeglasses sit a short distance away from your eye. Because you'll be looking through each lens from a slightly different distance, it's necessary to adjust the prescription accordingly. This ensures each type of corrective lens does its job from the appropriate distance.