How to Read a Contact Prescription

Similarities in Contact and Eyeglasses Prescriptions

If you wear eyeglasses, you may recognize some abbreviations or text from your eyeglass prescription as you review your new contact prescription. Whether you're wearing glasses or contacts, this information helps identify the type of lenses and the power of the lens you need. 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.

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.

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. 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.

Differences in Contact and Eyeglass Prescriptions

There are several differences between contact and eyeglass prescriptions. Here's how to make sense of it all.

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.

What An Eye Doctor Should Explain About Your Prescription

When you receive a prescription for contacts, your eye doctor should explain why they're prescribing a certain type of contact. For example, you may have an astigmatism that needs to be corrected. Or you may have a more complex prescription because you need contacts to help you see both near and far (multifocal lenses). EyeCare Associates provides several specialty contact lenses to help those with different eye conditions.Additionally, the prescription includes information about the contact lens brand that your eye doctor recommends. They may recommend a certain brand of contacts for many reasons, including the shape and curvature of your cornea, the complexity of your prescription, whether you have dry eyes or other factors. Your doctor should be interested to hear about what you're seeking from contact lenses. Together, based on your prescription and other factors, you should be able to find contacts that are comfortable, fit well and help with vision correction.Find a location and schedule an eye exam at EyeCare Associates to help determine which type of contact lens works best for you.