How to Read an Eyeglass Prescription

Do all those words on your prescription sound like Greek to you? Well, some of them are. But don't worry, we're here to teach you what it all means.

How to Read an Eyeglass Prescription

How to Read an Eyeglass Prescription

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Lens Types

Sphere Sphere Cylinder Axis Prism Base Add

Click on the prescription form to find out what all those number and abbreviations mean

To put it simply, your glasses prescription is a series of numbers, usually in a chart, and those numbers help us create lenses that will best correct your vision. Prescription charts typically have two rows—one for your right eye and one for your left—as well as five columns that are used to precisely describe your prescription. See, things are getting easier already.

The first thing you'll notice when you look at your prescription is a bunch of abbreviations. Here's what that shorthand means.

SPH or Sphere The “spherical error” refers to correction needed for nearsighted ( - ) or farsightedness ( + ). If you have a “+” starting at beginning of your spherical error that means you need to select Reading during the Rx process. There's a “-” you're going to probably want to pick Distance unless you know you're going to order multifocal lenses. The larger the number following the +/-, the stronger the prescription.

CYL or Cylinder Cylinder is needed to treat astigmatism, a refractive error if you like fancy words. It causes distorted and blurred vision which can result in headaches. Cylinder refers to the amount of lens power is need and is measured in quarters and proceeded by a ( + ) or ( - ).

AXIS The axis indicates the orientation of astigmatism, measured in degrees from 1 to 180.

ADD or NV ADD is the additive power needed for Meaning Near Vision, this is used to prescribe a multifocal or reading correction, measured in quarters. This power for bifocal or progressive lenses enlarges immediate vision and is therefore always indicated by a positive sign ( + ).

OD & OS The medical abbreviation OD, oculus dexter for you fans of Latin, refers to the right eye, whereas OS, or oculus sinester, is your left. Sometimes these two are simplified to R and L.

PD In order to customize your glasses, you have to figure out your PD, or pupillary distance, aka, the distance between your pupils. Once we have this information, we can determine how to place your lenses in your frame. Just ask your optician; they should have your PD on file. You can also measure your PD yourself.

PRISM Prism refers to the prismatic power used to correct vision displacement. It helps to reduce eyestrain and correct double vision.

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SPH (Sphere)

Spherical error, or overall power of lens is the basic part of your prescription. A (+) means you have trouble seeing near, and a (-) means you have trouble seeing things faraway.

CYL (Cylinder) & Axis

A cylinder value indicates astigmatisms or perpetually blurry vision. Axis—measured between 1 and 180°— tell us the orientation of the astigmatism

ADD (Addition)

This number is sometimes written NV for near vision and is used for multifocal lenses and readers

PD (Pupillary Distance)

It's just what sounds like—the distance in millimeters (mm) between your pupils. An average PD measurement is 63 mm, but varies by person. If it's not on the prescription, you can measure it yourself by printing our downloadable PD ruler.


We can process prism prescriptions to correct eye orientation

Vertical Prism is used to help correct vertical eye misalignments and is prescribed in opposite directions for both eyes

Horizontal Prism is used to help correct lateral eye misalignments and is always prescribed in the same direction for both eyes

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