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

You leave your eye test with a small card full of numbers, plus and minus signs, and letters like OD and CYL. Most people nod, pocket it, and never understand it. Here is what every part means, in plain language.

OD and OS: which eye is which

Your prescription is split into two rows. OD means your right eye and OS means your left eye. Some clinics simply write “Right” and “Left.” Each eye gets its own set of numbers because they are rarely identical.

SPH: the main strength

SPH, short for sphere, is the main power of your lens, measured in units called diopters. A minus number means you are nearsighted, so distance is blurry. A plus number means you are farsighted. The bigger the number, the stronger the correction. This is the number most Filipinos mean when they talk about their “grade.”

CYL and AXIS: your astigmatism

CYL, short for cylinder, describes astigmatism, which is when the eye is shaped a little more like a rugby ball than a basketball, so vision is blurred or stretched at certain angles. If this box is blank or says zero, you have little or no astigmatism.

AXIS always travels with CYL. It is a number from 1 to 180 that tells the lab the angle where the correction needs to sit. CYL tells you how much; AXIS tells you where.

ADD: the reading boost

ADD is extra magnifying power for close-up, added to the lower part of the lens. You will usually see it once you reach your forties, when reading up close gets harder. It is what makes reading and progressive lenses work.

PD: pupillary distance

PD is the distance between the centres of your pupils, in millimetres. It tells the lab exactly where the optical centre of each lens should line up with your eye. Get it wrong and even a perfect grade can feel off. This matters most with progressive lenses.

What about the plus and minus signs?

Do not panic over them. A minus SPH is nearsighted, a plus SPH is farsighted, and the signs simply tell the lab which way to grind the lens. What matters is that the whole prescription is copied exactly.

A quick example

• OD: -2.00 SPH, -0.75 CYL, 180 AXIS
• OS: -1.75 SPH, -0.50 CYL, 175 AXIS

This person is nearsighted in both eyes, with a small amount of astigmatism, slightly different in each eye. That difference is exactly why you should never split the difference with a ready-made pair.

Why the exact numbers matter

Rack-bought readers use one strength for both eyes and ignore astigmatism and PD. Your eyes are not identical, so lenses made to your full prescription simply feel clearer and more comfortable. A prescription also has an expiry for a reason: eyes change, and last year’s numbers may no longer be right.

The lens that uses every number on the card

A card full of precise numbers is only worth as much as the lens that carries them. Some lenses are made to your measurements. Others get close and hope you adjust.

Book a Vision7 eye test at your nearest Vision Express store. The seven-step exam measures everything on this list, SPH, CYL, AXIS, ADD and PD, and explains your results in language that actually makes sense.

Then ask for the Shamir Opulens Exact at the counter. It is made to your measurements, so your cylinder, axis and centring are cut to the numbers on your card instead of rounded to the nearest stock lens. That is what makes a prescription feel right from the first day rather than after a week of adjusting.

Every pair comes with free lifetime ultrasonic cleaning and free lifetime custom fitting and adjustment, so the optical centres keep lining up with your eyes long after you walk out.