How to Read Your Eyeglass Prescription

There are several different numbers on a typical eyeglass prescription. We think it’s important that our customers understand these measurements.

You should see two rows on your prescription, one labelled O.D. and the other labelled O.S.

• O.D. stands for Oculus Dexter and refers to your right eye’s measurements.
• O.S. stands for Oculus Sinister and refers to your left eye’s measurements.

Each eye will have boxes for 5 different measurements:

• Sphere (SPH) indicates the lens power prescribed for nearsighted or farsighted vision. Sphere is measured in diopter:
  .  + indicates farsightedness
  .   – indicates nearsightedness
• Cylinder (CYL) and Axis are measurements that are related to correcting Astigmatism. Both of these measurements will be filled out or both will be left blank.
• Add is an optional measurement that indicates magnifying power for reading, bifocal, multifocal and progressive lenses. For some prescriptions, this will be left blank.
• Prism (and Base) are measurements for eye alignment correction. For some prescriptions, this will be left blank.
• Pupillary Distance (PD) measures the distance between the centers of both pupils and is needed to correctly grind lenses. This measurement is usually taken by an optician in-store as part of the eyeglass purchase process.