If you need glasses, your eye-doctor will provide you with a prescription for corrective lenses. Eyeglass prescriptions may be written in different ways, though most are either printed or handwritten in horizontal rows. The first row is the prescription for the right eye (OD), and the second row is for the left eye (OS). Within each of these rows are three values: Sphere (SPH), Cylinder (CYL), and Axis. The SPH number corrects for nearsighted [indicated with a minus (-)] or farsighted [indicated with a plus (+)] vision. The CYL number and AXIS number correct for astigmatism. You may also have another field labeled as ADD which corrects for the reading power used in a bifocal or progressive lens. To learn more about how to read your prescription, click here. Lastly, eyeglass prescriptions sometimes include the pupillary distance (PD) measurement, which is the distance between your pupils. PD is needed to determine where the optical center of the lens will be for clear, accurate vision. If your prescription does not include your PD, you can measure it by yourself with our guide here. An eyeglass prescription will usually expire in 1-2 years, depending on which state you received your eyes exam.

Here’s a list of some optical abbreviations for you:

ADD (also NV-ADD): the Near Vision (NV) Reading ADDition correction on a multifocal Rx. It can be used for bifocal or progressive glasses, or for single-vision reading or computer (intermediate) vision glasses.

AR: Anti-Reflective. A coating that reduces reflection on the lenses.

AXIS: the angle at which the Cylinder (CYL) is placed on a lens to correct an astigmatism. It ranges from 1 to 180.

BAL: the Rx calls for balance lenses, meaning the same Rx for each eye. Often used when a person has no sight in one eye, so both lenses will have the same thickness.

BD, BI, BO, BU: a prism correction on your Rx (may be indicated with Δ, and one of these four abbreviations. The B stands for base, and it could be base down (BD), base in (BI), base out (BO), or base up (BU).

CYL: the Cylinder. Combined with the AXIS, the CYL corrects an astigmatism.

DS: the abbreviation for diopter simplex. An eye dr. may write DS on an Rx in the Cylinder (CYL) field if no astigmatism correction is needed.

DV: distance vision.

FT: flat-top bifocal.

NV: near vision.

NV-ADD (also ADD): the Near Vision (NV) Reading ADDition correction on a multifocal Rx. Can be used for bifocal or progressive glasses, or for single-vision reading or computer (intermediate) vision glasses.

OD: Latin for Oculus Dexter, meaning the right eye.

OS: Latin for Oculus Sinister, meaning the left eye.

OU: Latin for Oculus Uterque, meaning each eye.

PAL: Progressive Addition (or Adjustment) Lens: sometimes on a Progressive Rx an eye dr. will write two different numbers for the NV-ADD, perhaps +2.25 and +2.50, to increase the reading power in the NV-ADD for Progressive lenses.

PD (Pupillary Distance): the PD is the measurement of the distance between your pupils. This is needed for the manufacturer of the eyeglasses to know where to place the optical center on each lens, so you can see well with the glasses.

PL: Plano. Latin for "flat." If this is in the SPH section of an Rx, it means no nearsighted or farsighted correction is needed.

RX: a prescription.

SPH: the first section on an Rx. It corrects nearsighted or farsighted vision.

UV: the abbreviation of ultraviolet. UV light is invisible to the human eye, but it is UV light that gives us a sunburn, and too much exposure to it can damage the eyes.

VA: Visual acuity: how well the eye can see. Sometimes this may be written on an Rx, with a number such as 20/20. This would indicate that with eyeglasses made to this Rx, the vision would be corrected to 20/20 vision.