How to Read a Contact Lens Prescription

Key Abbreviations to Know

Your contact lens prescription may include several abbreviations. Here’s a breakdown of the most common ones:

• OD: Right eye 

• OS: Left eye 

• SPH or PWR: Spherical correction or power 

• Numbers with plus or minus signs: Diopters, a number that measures corrective lens strength. 

• CYL: Cylindrical power 

• Axis: The direction a cylindrical lens needs to be tilted. 

• DS: Diopters sphere 

• ADD: Additional correction 

Many of these abbreviations are also used in eyeglass prescriptions, but with contacts, they come with additional details. The number listed with SPH or PWR is in diopters and tells you how strong your corrective lens is. A plus sign (+) indicates farsightedness, and a minus sign (-) indicates nearsightedness.

If you have astigmatism, which happens when your cornea has an irregular shape, your prescription will also include "CYL," which indicates the strength needed to correct the astigmatism. "Axis" shows the orientation of the cylindrical lens to correct the shape. If you don’t have astigmatism, your prescription might show "DS," meaning your eyes have a regular, spherical shape.

Lastly, "ADD" indicates additional correction, which may be added to your prescription to include details about bifocals, multifocal lenses, or progressive lenses.

How is a Contact Lens Prescription Different from an Eyeglass Prescription?

While contact lens prescriptions include some similar abbreviations to eyeglass prescriptions, they also have additional measurements to account for the way contacts fit the eye. Here are some extra abbreviations you may encounter: 

• BC: Base curvature 

• DIA: Diameter 

"BC" refers to the curvature of your cornea. It’s important for the contact lens to match this curvature for proper fit and comfort. "DIA" describes the diameter of the contact lens, which is measured in millimeters. This helps ensure that the lens fits correctly on your eye.

Additionally, your contact lens prescription will include the brand of contacts prescribed and the expiration date for the prescription.

If you have both eyeglass and contact prescriptions, you might notice differences in the numbers, even for the same eye. This is because glasses and contacts are worn differently. Glasses sit a little distance away from your eyes, while contacts sit directly on your cornea. Because of these different distances, your prescriptions are adjusted to ensure the best vision correction in each case.

How Your Eye Doctor Will Explain Your Prescription

When you receive your contact lens prescription, your eye doctor will take the time to explain the reasoning behind their recommendations. For example, if you have astigmatism, they may recommend toric lenses to correct the condition, or if you need vision correction for both near and far distances, they might suggest multifocal lenses. EyeCare Associates offers various specialty contact lenses to cater to different eye conditions and needs.

Your prescription will also specify the brand of contact lenses your doctor recommends. The recommendation may be based on several factors, such as the shape and curvature of your cornea, the complexity of your prescription, whether you experience dry eyes, and other specific considerations.

Additionally, your doctor will discuss why you're choosing contacts instead of—or alongside—glasses. With your prescription and individual needs in mind, together you’ll find contact lenses that provide the best fit, comfort, and vision correction.