You've had your eye test, the optician has handed you a slip of paper, and it's full of numbers, plus and minus signs and abbreviations like SPH and CYL. If you're planning to buy glasses online, you'll need to understand it.
The good news: a glasses prescription only has a handful of parts. This guide explains each one in plain English, with real examples, so you can read your own prescription in a couple of minutes.
What a UK glasses prescription looks like
Most UK prescriptions are laid out as a small table, with one row for each eye:
|
Eye |
SPH |
CYL |
Axis |
Prism |
Base |
ADD |
|---|---|---|---|---|---|---|
|
R |
-2.25 |
-0.75 |
90 |
|
|
+2.00 |
|
L |
-1.75 |
-0.50 |
85 |
|
|
+2.00 |
R is your right eye and L is your left eye. Some prescriptions use the Latin terms OD (right) and OS (left) instead. Empty boxes are normal and simply mean you don't need that type of correction.
What each part of your prescription means
SPH (sphere) is the main strength of your lens, measured in dioptres.
- A minus (-) number means you're short-sighted: you see close up clearly, but distant things look blurry.
- A plus (+) number means you're long-sighted: distant things are clearer than close-up ones.
- The bigger the number, the stronger the lens. A -0.75 is a mild prescription; a -6.00 is a strong one.
- You may see Plano, Pl or ∞ instead of a number. That means no correction is needed for that eye.
CYL (cylinder) measures astigmatism, which happens when the front of your eye is shaped more like a rugby ball than a football. It makes vision blurry or distorted at all distances. If the CYL box is empty, or you see DS (dioptre sphere) next to SPH, you don't have astigmatism that needs correcting.
Axis is a number between 0 and 180. It tells the lab which direction your astigmatism runs, so they can position the correction correctly in the lens. You'll only see an Axis if there's a CYL value.
ADD (addition) is the extra magnifying power you need for reading and close work. It's always a plus number, usually between +0.75 and +3.00, and is common from your mid-40s onwards. An ADD value means you may need reading glasses, bifocals or varifocals.
Prism and Base correct problems with how your eyes work together, such as double vision. Most people don't have a prism value. If you do, your prescription will show a number (the prism strength) and a direction: Base Up, Base Down, Base In or Base Out.
You may also see distance (DV) and near (NV) rows, which give your prescription for distance glasses and reading glasses separately.
Glasses prescription examples, explained
|
Prescription (one eye) |
What it means |
Type of glasses |
|---|---|---|
|
SPH -1.50 |
Mildly short-sighted |
Distance glasses for driving, TV, screens across the room |
|
SPH +2.00 |
Long-sighted |
Glasses for close work, sometimes all day |
|
SPH -3.00, CYL -1.25, Axis 180 |
Short-sighted with astigmatism |
Single vision glasses with astigmatism correction built in |
|
SPH Plano, ADD +1.50 |
Clear distance vision, but needs help to read |
Reading glasses |
|
SPH -2.00, ADD +2.25 |
Short-sighted and needs help to read |
Varifocals or bifocals, or two separate pairs |
The numbers for each eye are often different, and that's completely normal. Your lenses are made separately for each eye.
Does a high number mean my eyes are bad?
Not necessarily. A higher number simply means you need a stronger lens. Prescriptions above about ±4.00 are considered moderate to strong. If yours is in that range, ask for thinner, high-index lenses. They keep your glasses lighter and stop the edges looking thick, especially in rimless or semi-rimless frames.
Your right to a copy of your prescription
In the UK, the Opticians Act 1989 says your optician must give you your prescription straight after your sight test, whether it's an NHS or private test. You don't have to buy your glasses from them. You're free to take that prescription anywhere, including online.
If you've lost your copy, contact the optician who tested your eyes and ask for it.
Is pupillary distance (PD) on my prescription?
Usually not. Your pupillary distance (PD) is the distance between the centres of your pupils, in millimetres. It's needed to line up your lenses correctly, but in the UK it isn't legally part of the prescription, so many opticians leave it off.
You can ask your optician to measure it and write it down, or measure it yourself at home with a ruler and a mirror. Most adults have a PD between 54mm and 74mm.
Glasses prescription FAQs
How long is a glasses prescription valid for in the UK? There's no fixed legal expiry date, but most adults are advised to have an eye test every two years. Your prescription will show the test date, and online retailers generally ask for one from the last two years. Read more in our guide on how often you should get an eye test.
Is a glasses prescription the same as a contact lens prescription? No. Contact lenses sit directly on your eye, so the numbers are different and the prescription includes extra measurements. You can't use a glasses prescription to order contact lenses.
What does a minus number mean on a glasses prescription? A minus number in the SPH box means you're short-sighted. Distance vision is blurry, and close-up vision is usually clear.
What does ADD mean on my prescription? ADD is extra magnifying power for reading. If you have an ADD value, you need reading glasses, bifocals or varifocals.
Can I use an NHS voucher with my prescription online? If you're eligible for an NHS optical voucher, you can put it towards your glasses at Specsmart. See our NHS voucher page for details.
Order glasses online with your prescription
Now that you can read your prescription, buying glasses online is simple. Choose your frames, enter your SPH, CYL, Axis and ADD for each eye, and we'll make your lenses to match.
No prescription yet? Book a free eye test. Not sure about a frame? Try it with our free home trial, backed by 30-day free returns.
