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How to read your prescription?

It is important to find the right prescription type for your eyes before you buy eyeglasses. Let’s take the following data as an example:

Note: The prescription for contacts CANNOT be used for eyeglasses.

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

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

OU - Latin for Oculus Uterque, meaning both eyes.

SPH - Sphere, the degree of correction, it corrects your near (+) or farsightedness (-).

CYL - Cylinder, it corrects your astigmatism. It will be 0 if you don’t have astigmatism.

AXIS - the angle at which the Cylinder (CYL) is placed on a lens to correct an astigmatism. It ranges from 1 to 180. NO CYL, NO AXIS

ADD - Addition or Near Vision (NV), it is calculated for getting the correction for reading or near vision, it can be used for bifocal or multifocal progressive glasses.

PRISM - Prismatic value, it is needed to compensate for any alignment problems in your eyes (e.g. double vision or “lazy eye”). 

BASE - The direction of a prism. May indicated with Δ, and one of these four abbreviations. Base up (BU), base down (BD), base in (BI), or base out (BO).

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. PD can be written in different ways: e.g., 66 (Single PD), 33/33 (Dual PD), or 66/64(Distance PD/Near PD).

VA - Visual acuity. How well the eye can see. Sometimes this may be written on an Rx, with a number such as 6/6. This would indicate that with eyeglasses made to this Rx, the vision would be corrected to 6/6 vision.

Now that you know what these terms mean, you know how to read a glasses prescription, which is the most important part of learning how to buy prescription glasses online.