Prescription guide
A form full of codes. Decoded.
Your prescription is shorter than it looks: four numbers per eye and one for the space between them. Here is what each one means, in plain English.
The four numbers
What your optician wrote down.
SPH
Sphere
The main power of the lens, in 0.25 steps. Minus (−) corrects distance short-sightedness, plus (+) corrects long-sightedness. This is the number that matters most.
CYL
Cylinder
How much astigmatism correction you need, if any. Zero or blank means none. It is always paired with an axis.
AXIS
Axis
The angle the cylinder sits at, from 0 to 180 degrees. Only meaningful alongside a CYL value.
ADD
Reading addition
The extra near power for reading glasses or progressives. Usually only present if you are over 40.
UK prescriptions are usually written for both eyes, right (R or OD) and left (L or OS). Copy each column exactly. Prescriptions are typically valid for two years after your last sight test.
PD, in 30 seconds
Measure your pupil distance with a mirror.
PD is the distance between your pupils in millimetres, usually 58 to 66 for adults. It is often left off the prescription, so here is the fast way to get it yourself.
- 1
Stand about 30cm from a mirror, looking straight ahead.
- 2
Hold a ruler against your eyebrows, resting on the bridge of your nose.
- 3
Close your right eye and line the zero up with the centre of your left pupil.
- 4
Open both eyes, close your left eye, and read the millimetres under your right pupil.
- 5
That number is your PD. Repeat twice to be sure it matches.
Somewhere between two pupils? Adult PDs almost always fall between 58 and 66mm. If yours reads far outside that, measure again.
How try-on works
Your camera, your face, nothing stored.
The live try-on runs entirely in your browser. Your camera feed is processed on your device to find your eyes and place the frame at true scale. Nothing is recorded, uploaded or sent anywhere.
If the camera is not an option, upload any photo of yourself and position the frame by hand. It works just as well, and the photo never leaves your device either.
Got all that? You are ready.
Pick a frame, try it on, then send your prescription whichever way suits you.