Demystifying Your Prescription

Anatomy of a Prescription

You’ve found the perfect frame, you’ve been to the eye doc and you have a prescription in hand. OD, OS, SPH, CYL, PD—say what? Let’s clarify what it all means.

Rollover the sample Rx to learn more.

PRISM & BASE

This is added to some eyeglasses to compensate for eye alignment problems.

If you have values in your Prism columns, you’ll need to have a local eye clinic add corrective lenses to frames you purchase from us.

AXIS

A number between 1 and 180 that indicates the cylinder power in the lens necessary to correct your astigmatism.

CYLINDER (CYL)

The amount of lens power needed to correct astigmatism. If no number is provided you don’t have astigmatism, or your eye doc feels there is such a small amount that it’s unnecessary to correct it.

A minus sign (–) means nearsighted astigmatism. A plus sign (+) means farsighted astigmatism.

Currently we can work with prescriptions that have a CYL value between -3.00 and +3.00. If yours is outside that range, we’ll help you find frames here and then you buy corrective lens from your local eye clinic.

SPHERE (SPH)

The amount the lens must provide to sharpen your distance vision to an acceptable level (usually 20/20). A minus sign (–) indicates nearsightedness (myopia). A plus sign (+) means farsightedness (hyperopia).

The farther these numbers are from zero, the greater the amount of correction you need.

ADD

Magnifying power added to the distance prescription in the lower half of multifocal lenses to restore near vision.

This section is usually left empty but if there is a number, it means you need bifocals or progressive lenses.*

*Currently we cannot fill prescriptions for these types of lenses. You can order any of our frames with our demo lenses and then you can visit your local eye clinic for the correct lenses.

DISTANCE

The lens power prescribed to help you see distant objects clearly. The values are determined from the results of viewing an eye chart through various test lenses.

OD & OS

Abbreviations for oculus dexter and oculus sinister, Latin for right eye (OD) and left eye (OS). Poor lefty got saddled with a rather unfortunate name.

Fun Fact: Why The Right Eye Comes First
On your prescription, it’s common for the values for the right eye (OD) to come before the left eye (OS). Eye docs write prescriptions this way to avoid making errors. Like looking at yourself in a mirror, doctors read your face from right eye to left eye.

PUPILLARY DISTANCE (PD)

Pupillary distance (PD) is the distance in millimeters between the center of each pupil. This measurement verifies where to concentrate the power of your correction.

Why Your PD Might Be Missing

In the course of a typical eye exam, optometrists and ophthalmologists may not measure your pupillary distance. This is usually handled by an optician before you order a new pair of eyeglasses. Most eye clinics will happily measure your PD for you, even post-exam.

We recommend that you have your PD measured professionally. Even if it is not written directly on your prescription, your PD may be on file with your doctor or the last place that made your prescription glasses.

Your Eyes, Your Prescription

The Federal Trade Commission’s Prescription Release Rule is a law that requires eye doctors to give you a copy of your eyeglass prescription after an exam. The rule protects the "portability" of your eyeglass prescription, allowing you to use it to buy glasses from the vendor of your choice. If you feel your eye doctor isn’t being fair about your prescription, you can contact the FTC at (877) 382-4357.