How to read your eyeglass prescription: SPH, CYL, AXIS and ADD explained

You finish your eye test, you get a small card full of numbers and abbreviations, and it may as well be in code. If you have ever squinted at your prescription wondering what OD, OS, SPH, or CYL actually mean, here is a plain-language guide to reading it.

OD and OS: which eye is which

These come from Latin. OD (oculus dexter) is your right eye. OS (oculus sinister) is your left eye. Some clinics simply write R and L. Each eye gets its own row of numbers because your two eyes are rarely identical.

SPH (Sphere): your main grade

SPH is the number Filipinos usually mean when they say their grade. It is measured in units called diopters. A minus sign means you are nearsighted (myopia), so distant things look blurry. A plus sign means you are farsighted (hyperopia). The bigger the number, the stronger the correction, so -3.00 is a stronger nearsighted grade than -1.00.

CYL and AXIS: your astigmatism

If you have astigmatism, the front of your eye is shaped a little more like a rugby ball than a basketball, so light focuses unevenly.

• CYL (Cylinder) is the amount of astigmatism correction you need. A blank space or DS here usually means no astigmatism.
• AXIS is a number from 1 to 180 that tells the lab which direction the cylinder correction should sit. It always travels together with CYL.

ADD: for reading and progressives

ADD is extra magnifying power added to the lower part of the lens to help with close-up work. You usually see it once presbyopia sets in, the normal, age-related change that makes near focus harder from around your forties. ADD is what makes reading glasses, bifocals, and progressive lenses work.

PD: the measurement that centers your lenses

PD (pupillary distance) is the gap between the centers of your pupils, in millimeters. It is not always printed on your prescription, but the lab needs it to line up the optical center of each lens with your eyes. Get it wrong and even a perfect grade can feel off.

A few honest cautions

• Your prescription is specific to you and to the date it was measured. Grades change, so an old slip may no longer be accurate.
• A prescription for glasses is not the same as one for contact lenses. Contacts sit on the eye and need their own fitting and measurements.
• Reading numbers off a card does not replace an exam. The numbers are the output of a careful process, not something to self-adjust.

Want yours explained properly?

Book a Vision7 eye test at your nearest Vision Express store. The seven-step exam ends with your optometrist walking you through every figure on the card in plain language, so SPH, CYL, AXIS and ADD stop being code and start meaning something about your eyes.

Then ask for the Shamir Opulens Exact at the counter. Most lenses round your grade to the nearest standard step, which quietly throws away part of what the exam just measured, especially your cylinder and axis. This one is made to the exact figures on your prescription. The numbers you just had explained are the numbers sitting in front of your eyes.

We take your PD in store as well, because a correct grade in a badly centered lens still feels wrong. Every pair comes with free lifetime ultrasonic cleaning and free lifetime custom fitting and adjustment.