A multifocal contact lens prescription contains all the same values as a standard contact lens prescription, plus an additional “ADD” power that corrects your near vision. Once you know what each abbreviation stands for and what the numbers mean, the whole thing becomes straightforward to read.
Eye Identifiers: OD, OS, and OU
Every prescription lists values separately for each eye. OD refers to your right eye (from the Latin “oculus dexter”), and OS refers to your left eye (“oculus sinister”). You may occasionally see OU, which means both eyes together. Your right and left eyes almost always have different correction values, so each row on your prescription will have its own set of numbers.
Power (PWR or SPH)
This is the main correction strength, labeled either PWR or SPH (for “sphere”). It’s measured in diopters and tells you how much correction you need for distance vision. A minus sign means you’re nearsighted, and a plus sign means you’re farsighted. The number increases in 0.25-diopter steps (so you might see -2.25, -2.50, -2.75, and so on). At higher strengths, typically above +6.00 or -6.00, the steps may jump to 0.50 diopters, though this varies by brand.
If your value is “plano” or “0.00,” that eye doesn’t need distance correction, but you may still need the multifocal ADD power for reading.
The ADD Power: What Makes It Multifocal
The ADD value is the defining feature of a multifocal prescription. It represents the extra magnification built into the lens for close-up tasks like reading, using your phone, or working at a computer. This is the correction that replaces reading glasses.
Unlike standard power, ADD values on contact lens prescriptions are usually expressed as categories rather than exact numbers. Most brands use a system like Low (LO), Medium (MED), and High (HI). Low corresponds to a smaller amount of near correction, suitable for people just beginning to notice difficulty reading up close. High is for those who need more significant help with near vision. Your eye care provider determines which category fits based on a separate measurement of your near-vision needs.
Some prescription forms list the ADD as a numerical diopter value (like +1.50 or +2.00), which your provider then matches to the appropriate category for your specific lens brand. You don’t need to convert between the two yourself, but if you see both on your paperwork, that’s what’s happening.
Dominant Eye Designation
Many multifocal prescriptions also note which of your eyes is dominant, sometimes marked as “D” for dominant and “N” for non-dominant. This matters because some multifocal lens designs are optimized differently for each eye. Your dominant eye may get a lens weighted more toward distance clarity, while your non-dominant eye gets slightly more near-vision emphasis. This pairing helps your brain blend the two images into comfortable vision at all distances.
Base Curve and Diameter
These two values describe the physical shape and size of the lens, not your vision correction. Base curve (BC) indicates how curved the back surface of the lens is, measured in millimeters. For soft contact lenses, this typically falls between 8.0 and 9.5 mm, with 8.6 mm being a common standard. It needs to match the curvature of your cornea so the lens fits comfortably and stays centered.
Diameter (DIA) is the overall width of the lens across its face. Soft lenses usually range from 13.0 to 14.5 mm. Both values are determined during your fitting and must match what’s on your prescription when you order lenses. Even a small mismatch can cause discomfort or blurry vision.
Brand Name
Contact lens prescriptions are legally required to specify a brand. This isn’t a suggestion or a preference. Under federal rules enforced by the FTC, a seller cannot substitute a different brand without the prescriber’s approval. The brand matters more than you might think with multifocal lenses because each manufacturer uses a different optical design to deliver near and distance correction. Some use a concentric design, where near and distance zones are arranged in a bull’s-eye pattern. Others use an aspheric design, where both corrections blend gradually across the center of the lens. These designs aren’t interchangeable, and switching brands could significantly change how well you see.
Why It Differs From Your Glasses Prescription
If you compare your multifocal contact lens prescription to your glasses prescription, you may notice the power values don’t match. This is normal. Eyeglasses sit about 12 to 14 millimeters away from your eyes, while contact lenses rest directly on your cornea. That gap, called vertex distance, changes the effective strength of the lens. For prescriptions stronger than about +4.00 or -4.00 diopters, your eye care provider performs a calculation to adjust for this difference. A glasses prescription of -5.00 might translate to a contact lens power of -4.75, for example. You can’t simply use your glasses numbers to order contacts.
Your glasses prescription may also include a cylinder value and axis for astigmatism correction. Standard multifocal contact lenses don’t correct astigmatism, so those values won’t appear. If you do have astigmatism, you may need a multifocal toric lens, which is a more specialized category with additional parameters.
Reading a Sample Prescription
Here’s what a typical multifocal contact lens prescription might look like in practice:
- OD (right eye): PWR -3.25, ADD LO, BC 8.6, DIA 14.2
- OS (left eye): PWR -2.75, ADD LO, BC 8.6, DIA 14.2
- Brand: [specific lens name]
This tells you the right eye needs -3.25 diopters of distance correction with a low ADD for near vision, and the left eye needs -2.75 diopters with the same low ADD. Both lenses have an 8.6 mm base curve and a 14.2 mm diameter. When ordering, every single one of these values needs to match exactly. Changing even the ADD category from Low to Medium would give you a different lens that your provider didn’t prescribe.
Prescription Expiration
Contact lens prescriptions have a set expiration date, typically one to two years depending on your state’s laws. After that date, sellers cannot legally fulfill your order, and you’ll need a new eye exam. The expiration date should be printed on the prescription itself. Keeping track of this is especially important with multifocal lenses, since your ADD power needs tend to increase gradually over time and an outdated prescription may no longer give you clear near vision.