Understanding Your Contact Lens Prescription

Common Abbreviations in Your Contact Lens Prescription

Your contact lens prescription will typically include several abbreviations. Here’s a guide to the most common ones you’ll encounter:

• 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 

While many of these abbreviations are also used in eyeglass prescriptions, contact prescriptions have additional details. The number next to SPH or PWR is in diopters and shows the strength of your lens. A plus (+) sign means farsightedness, while a minus (-) sign indicates nearsightedness.

For those with astigmatism, which occurs when your cornea has an irregular shape, your prescription will include “CYL,” which indicates how much cylindrical power is needed to correct the condition. “Axis” shows the direction the cylindrical lens should be positioned. If you don’t have astigmatism, your prescription may show “DS,” meaning your eyes have a normal spherical shape.

Lastly, “ADD” is added to your prescription if you need additional correction for bifocal, multifocal, or progressive lenses. 

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

Although contact lens prescriptions share some abbreviations with eyeglass prescriptions, they also contain additional measurements to accommodate how contacts fit on your eye. Here are a couple of extra abbreviations you may find:

• BC: Base curvature 

• DIA: Diameter 

The “BC” refers to the curvature of your cornea, which must match the curvature of your contact lenses for a proper fit and comfort. “DIA” measures the diameter of the contact lens in millimeters, ensuring a correct fit.

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

If you have both eyeglass and contact prescriptions, you may notice that some numbers are different even for the same eye. This is because glasses and contacts sit on your eyes in different ways—glasses rest a short distance from your eyes, while contacts sit directly on your cornea. Due to these differences, your prescriptions are adjusted to provide the best possible vision correction for each type of lens.

How Your Eye Doctor Will Explain Your Prescription

When you receive your contact lens prescription, your eye doctor will take the time to explain why they've selected a particular type of lens for you. For instance, if you have astigmatism, they may recommend toric lenses to correct the irregular shape of your cornea. If you need help with both near and far vision, multifocal lenses may be the best option. The EyeDoctors Optometrists offers various specialty contact lenses designed to meet a range of vision needs.

Your prescription will also include the brand of contact lenses that your doctor recommends. This decision is based on several factors, including the shape of your cornea, the complexity of your prescription, any issues with dry eyes, and other personal considerations.

Additionally, your doctor will discuss why you've chosen contact lenses over glasses or why you may want to use them together. Together, based on your specific prescription and needs, you’ll choose the contact lenses that offer the best fit, comfort, and vision correction.