How to Read Your Eyeglass Prescription

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.
Did you know that eyeglass prescriptions expire? Most prescriptions are valid for two years before you require a new eye exam and prescription. It’s important to note that we cannot legally dispense eyeglasses without a valid prescription.
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