Understanding your prescription shouldn’t be complicated.

Your prescription simply describes how your lenses need to be made.

This guide explains what the numbers mean, so you can enter your details with confidence and without second-guessing.

What a prescription actually is

A glasses prescription is a set of measurements that tells us how light needs to be adjusted for your eyes.

Your prescription helps lenses:

  • Bring images into focus
  • Reduce strain and fatigue
  • Feel natural during everyday wear

When entered correctly, you shouldn’t notice your lenses working — they should just feel clear.

The main numbers, explained simply

Most prescriptions include a few core values. You don’t need to memorise them — just recognise what they relate to.

  • SPH (Sphere): Corrects short- or long-sightedness.
  • CYL (Cylinder): Corrects astigmatism (how evenly light enters the eye).
  • AXIS: Works with CYL to fine-tune astigmatism correction.
  • ADD: Used for reading or multifocal lenses, usually for near vision support.

Each value plays a specific role — changing one changes how the lens performs.

Left and right eyes are treated separately

Your prescription will list values for:

  • OD (right eye)
  • OS (left eye)

It’s very common for these to be different.

Lenses are made individually for each eye to ensure balance, comfort, and clarity — even small differences matter.

Pupillary distance (PD)

PD measures the distance between your pupils.

It helps ensure:

  • Clear central vision
  • Balanced focus across both lenses
  • Reduced eye strain

If your PD isn’t listed on your prescription, it can usually be measured quickly at home or by your optician. Check out our guide learn how to measure your PD.

Accurate PD helps lenses feel natural from the moment you put them on.

Reading your prescription correctly

Prescriptions are written by professionals, but they’re not always laid out the same way.

Things to watch for:

  • Plus (+) and minus (–) signs
  • Separate rows for each eye
  • Whether ADD is included

If something looks unfamiliar, it doesn’t mean it’s wrong — it just means it needs to be entered carefully.

Prefer us to handle it for you?

If you’d rather not enter your prescription yourself, you don’t have to.

You can upload a photo or scan of your prescription, and we’ll take care of the details for you — checking everything for accuracy before your lenses are made.

You’ll still have the final say, without the stress of getting the numbers wrong.

Optician-led always

Every prescription at OpticalGlasses is reviewed with clarity, comfort, and everyday wear in mind.

If something doesn’t feel right once your glasses arrive, we’ll help you check the details and get things corrected.

You shouldn’t have to guess — and you won’t be left on your own.