How to read your eyeglass prescription

You get your prescription after an eye test, glance at the grid of numbers and abbreviations, and feel none the wiser. It looks technical, but it is really just a short set of measurements for each eye. Once you know what each column means, your prescription becomes readable in about a minute. Here is the whole thing, decoded.

OD and OS: your two eyes

The first thing you will see is two rows, usually labeled OD and OS. These come from Latin. OD is your right eye and OS is your left. If you see OU, that means both eyes together. Your two eyes almost always have slightly different numbers, which is completely normal.

SPH: the main correction

SPH stands for sphere, the core of your prescription. It tells you how much lens power you need to see clearly. A minus value means you are nearsighted, so distance is blurry. A plus value means you are farsighted. The bigger the number, the stronger the correction. A -1.00 is mild; a -5.00 is stronger.

CYL and axis: astigmatism

If your prescription has values under CYL and axis, you have some astigmatism, which simply means your eye is shaped a little more like a rugby ball than a perfect sphere. It is very common. CYL is the amount of correction needed, and axis, a number from 1 to 180, tells the lab the angle to place it. The two always work as a pair. If CYL is blank, you have little or no astigmatism.

ADD: help for reading

ADD appears when you need extra power for close-up work, typically from your forties onward as near focus naturally gets harder. It is the same in both eyes and always a plus value. ADD is what makes reading glasses, bifocals, and progressive lenses possible.

PD: pupillary distance

PD is the distance between the centers of your pupils, measured in millimeters. It makes sure the optical center of each lens sits right in front of your eye. Get it wrong and even a correct prescription can feel off. This is one reason lenses are best fitted in person.

What your prescription does not tell you

Here is the part worth remembering. Your prescription is a snapshot of how to correct your vision. It does not describe the health of your eyes. It says nothing about eye pressure, the retina, or early signs of disease that show no symptoms. That is why a number on a card is not a substitute for a full exam.

A prescription also has a shelf life. Eyes change, and an old grade can leave you squinting or straining without realizing why. If yours is more than a year or two old, it is worth rechecking.

Get the full picture

Reading your prescription is a useful skill, but it is only one page of a longer story.

Book a Vision7 eye test at your nearest Vision Express store. The seven-step exam measures your grade precisely, checks that your eyes work together and screens your eye health, so you leave with a prescription you understand and know is current. Then ask for the Shamir Opulens Exact at the counter. It is made to your exact measurements, including your PD, so the optical centre lands where your eyes actually look and every number on that card is used the way it was meant to be. Many prescriptions are ready in 30 minutes. Free lifetime ultrasonic cleaning and free lifetime custom fitting and adjustment come with every pair.