After an eye test, if you need glasses, the optometrist writes you a prescription. It is usually a small table with a row for your right eye (R) and your left eye (L), and columns such as SPH, CYL, Axis and ADD.
By law, the optician must give you a copy of your prescription after your sight test, and you can use it to buy glasses anywhere you like. Type your numbers into the decoder below to see what they mean.
Decode your glasses prescription
Copy the numbers from your prescription. Leave boxes blank if they are empty on yours. Nothing you enter is saved or sent anywhere.
Right eye (R)
Left eye (L)
This explains what the numbers mean. It cannot check whether your prescription is right for you, and a glasses prescription cannot be used to buy contact lenses.
What each part of your prescription means
| Term | What it means |
|---|---|
| R and L | Right eye and left eye. Older prescriptions may say OD (right) and OS (left) |
| SPH (sphere) | The main lens power, in dioptres. Minus means short-sighted, plus means long-sighted |
| CYL (cylinder) | Extra power to correct astigmatism. Blank if you do not have astigmatism |
| Axis | The direction of the astigmatism correction, from 1 to 180 degrees. Only used with a CYL value |
| ADD | Extra magnifying power for reading and close work, used in reading glasses, bifocals and varifocals |
| Prism | Helps your eyes work together, written with a direction such as up, down, in or out |
Your right to your prescription
Under the Opticians Act, the optometrist must give you a signed prescription after your sight test, or a statement that you do not need glasses. You do not have to buy your glasses from the same optician.
Glasses and contact lens prescriptions are different
A glasses prescription cannot be used to buy contact lenses. Contact lenses need a separate fitting and a contact lens specification from a registered optometrist, contact lens optician or doctor.
How long a prescription lasts
Your prescription shows what you needed on the day of your test. Most adults are advised to have an eye test every 2 years, or more often if your optometrist recommends it, because your eyes and prescription can change.
