A Simple Guide to Read Your Eyeglass Prescription

If you’ve ever been handed a new eyeglass prescription and felt a bit lost, you’re not alone. Prescriptions use specific abbreviations and numbers that can seem complicated at first. Here’s a guide to help you interpret the meaning behind each element on your eyeglass prescription, so you can better understand your eye health and lens needs before coming to Frame Of Choice.

Your prescription will likely start with OD and OS:

• OD is short for oculus dexter, meaning "right eye."
• OS stands for oculus sinister, which refers to the "left eye."
• Occasionally, you may also see OU (oculus uterque), meaning "both eyes."

2. SPH (Sphere): Correcting Nearsightedness or Farsightedness

The SPH (sphere) number indicates the primary corrective power required for each lens, measured in diopters:

• A negative (-) SPH corrects nearsightedness (myopia), meaning you see objects up close clearly but struggle with distance.
• A positive (+) SPH is for farsightedness (hyperopia), which means you see distant objects well, but close-up tasks might be challenging​

For those with astigmatism, your prescription will include CYL and Axis values:

• CYL corrects astigmatism, an imperfection in the eye's shape that causes blurred vision. A negative CYL value indicates nearsighted astigmatism, while a positive value is for farsighted astigmatism.
• Axis is a number from 1 to 180 degrees, specifying the orientation for the cylindrical correction. For instance, if your CYL is -1.00 with an Axis of 90, this means your astigmatism correction is oriented vertically​

If you see an ADD value on your prescription, it’s the additional magnifying power required for near-vision tasks like reading. This is commonly seen in bifocal or progressive lenses and helps with presbyopia, a common age-related condition affecting near vision. ADD is always a positive number, typically ranging from +0.75 to +3.00 diopters​

Prism correction is not on every prescription. It’s usually prescribed for eye alignment issues, like strabismus or double vision. The Prism value is measured in prism diopters and often paired with a Base direction:

• Base Up (BU) or Base Down (BD) corrects vertical misalignments.
• Base In (BI) or Base Out (BO) corrects horizontal alignment issues​

6. PD (Pupillary Distance): Aligning the Lenses with Your Eyes

PD (pupillary distance) is measured in millimeters and is the space between the centers of your pupils. This measurement ensures the optical centers of your lenses align with your eyes for optimal vision, especially for stronger or progressive prescriptions​

With this guide, you can now understand the main elements in an eyeglass prescription. Knowing what these terms mean is helpful for interpreting the specific needs your eye doctor identified. Remember to always keep an updated prescription, as vision needs can change over time.