How to Read Your Glasses Prescription
Your prescription can look like a wall of abbreviations and minus signs, but it only takes a few minutes to understand. This guide walks through each part in plain English, so you can enter it confidently when you order prescription lenses from us.
The two rows: right and left
Prescriptions are written per eye. OD (or R / Right) is your right eye; OS (or L / Left) is your left. The two eyes are often different — that's completely normal.
SPH (Sphere)
SPH is the main strength of the lens, measured in dioptres. A minus number (e.g. −2.00) corrects short-sightedness — distant things look blurry. A plus number (e.g. +1.50) corrects long-sightedness — close-up things are harder to focus on. The bigger the number, the stronger the lens. Some prescriptions show 0.00, “Plano” or “PL”, which simply means no correction is needed for that part.
CYL (Cylinder) and AXIS
CYL corrects astigmatism — when the front of the eye is shaped slightly more like a rugby ball than a football, which blurs vision at certain angles. The AXIS (a number from 1 to 180) tells the lab which direction that correction needs to sit in the lens. CYL and AXIS always come as a pair: if you have a CYL value, you must also have an AXIS. If both are blank, you have no astigmatism correction — that's fine, just leave those boxes empty.
PD (Pupillary Distance)
Your PD is the distance between the centres of your pupils, in millimetres — typically between 50 and 75mm for adults. It makes sure the optical centre of each lens lines up exactly with your eye. It may be written as one number (e.g. 62) or two halves (e.g. 31/31, one per eye).
PD isn't always printed on prescription cards. If yours is missing, you can ask wherever you had your sight test — or use the camera PD tool built into every frame page on our site. It measures your PD in seconds using your device's camera, processed entirely on your device.
Other things you might see
ADD (Addition) is the extra power for reading, used for bifocal or varifocal lenses. Prism corrects how the eyes work together and appears only on a small number of prescriptions. If your prescription includes either and you're unsure what to order, add a note at checkout and our eyewear specialists will check it for you before anything is made.
Before you order
UK rules require prescriptions used for ordering glasses to be under two years old, and we glaze lenses for wearers aged 16 and over. Double-check every number and sign (+ / −) against your prescription card — a photo of the card in the order notes never hurts. Our specialist glazing lab checks every order before it's made, and we'll contact you if anything looks unusual.