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

You leave your eye test with a small card full of numbers and short codes, and most people file it away without knowing what it says. Understanding it helps you order the right lenses, compare an old grade with a new one, and ask better questions. Here is what each part means.

OD and OS: your two eyes

Your prescription is split by eye. OD means the right eye and OS means the left, from the Latin terms opticians still use. Some cards simply write Right and Left. Each eye gets its own set of numbers because they rarely need exactly the same correction.

SPH: the main power

SPH, short for sphere, is the main strength of the lens, measured in units called diopters. A minus value means you are nearsighted, so distant objects blur while near ones stay clear. A plus value means you are farsighted. The further the number sits from zero, the stronger the correction. A -1.00 is mild; a -5.00 is stronger.

CYL and AXIS: astigmatism

If your card has numbers under CYL and AXIS, you have some astigmatism, which simply means the front of your eye is shaped a little more like a rugby ball than a basketball. CYL (cylinder) is the extra power needed to correct it. AXIS is a number from 1 to 180 that tells the lab the angle to place that correction. The two always appear together. Astigmatism is common and fully correctable, so seeing these numbers is nothing to worry about.

ADD: help for near vision

ADD is an added magnifying power for close work, usually printed once you reach your forties and near focus starts to fade. It is the figure behind reading glasses and progressive lenses. If your card shows an ADD, it means the same pair can be built to help you see both far and near.

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 directly in front of each eye. A wrong PD can leave you with lenses that feel off or cause eye strain, which is one reason a proper fitting matters as much as the grade itself.

Why the numbers are only half the story

A prescription tells the lab what to make, but it does not choose the lens for your life. The same grade can go into a thin lens for a strong prescription, a lens with anti-reflective coating for night driving, or a progressive lens for someone who switches between a laptop and the road all day. That choice depends on how you actually use your eyes.

Prescriptions also expire. Vision drifts over months and years, and an old card can send you home with lenses that no longer match your eyes.

What to ask for at the counter

Book a Vision7 eye test at your nearest Vision Express store. The seven-step exam gives you a current card you can trust, with SPH, CYL, AXIS, ADD and your PD all measured properly rather than carried over from an old pair.

Then ask for the Shamir Opulens Exact at the counter. It is cut to your exact numbers rather than rounded to the nearest stock power, so your CYL and AXIS land where they should and the lens stays clean right to the edges instead of only in the middle. If your grade is on the stronger side, that precision is what keeps the lens thinner and the view honest.

Single vision lenses are ready in 30 minutes, and frames in stock are yours in 20. Bring the pair back any time for free lifetime ultrasonic cleaning and free lifetime custom fitting and adjustment, because a correct PD only helps if the frame stays sitting where we set it.