How to Read Your Eyeglass Prescription: A Complete Guide

Just received an eyeglass prescription from your eye doctor? The numbers and abbreviations can look confusing at first. This guide from Cinily Glasses explains the key terms to help you understand the information needed when ordering prescription glasses online.

Decoding the Key Terms

Your prescription usually lists each eye separately: OD (right eye) and OS (left eye). Here is what the main columns mean. ^[1]

• SPH (Sphere)
  SPH is the spherical lens power, measured in diopters. In a distance prescription, a minus sign (-) indicates correction for nearsightedness (myopia), while a plus sign (+) indicates correction for farsightedness (hyperopia). ^[1]
• CYL (Cylinder) & AXIS
  CYL specifies the lens power for astigmatism, and AXIS specifies the correction's orientation in degrees. Astigmatism involves the shape of the cornea or lens. A blank CYL field generally means no cylinder correction is specified on that prescription; it does not mean your eyes are perfectly spherical. ^{[1] [2]}
• ADD (Addition)
  ADD is extra lens power added to the distance correction for close-up tasks. It may appear when prescribing reading lenses or multifocal designs such as progressive lenses. The ADD value alone is not a complete reading prescription. ^[1]

Before ordering: Copy the values for each eye exactly as written, including plus and minus signs. Ask your eye doctor to clarify any unclear entry rather than guessing or changing it yourself.

The Missing Detail: What Is PD?

Pupillary distance (PD) is the distance between the centers of your pupils, measured in millimeters. It helps position your prescription lenses correctly in front of your eyes. PD may not appear on your prescription, so ask your eye care provider whether a measurement is available. ^[3]

For an introduction to home measurement, see our Step-by-Step PD Measurement Guide. Home readings can vary. For progressive lenses or uncertain results, have an eye care professional confirm your measurements. ^[3]