RefraCard
RefraCard · Learn
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Nineteen short guides. What each number on a prescription means, the conditions those numbers describe, and the questions people actually ask when they are holding the paper.
Your prescription, number by number
One guide per value on the paper.
SPH — sphereThe main power of the lens. Minus corrects short-sightedness, plus corrects long-sightedness.
CYL — cylinderYour astigmatism — how far from perfectly round the front of the eye is.
AXISA direction from 1° to 180°, not a strength. 175 is not “more” than 12.
ADD — near additionThe extra plus for close work, once focusing stiffens from the mid-forties.
PD — pupillary distanceThe millimetres between your pupils — what centres the lenses in front of your eyes.
Prism and baseOn a minority of prescriptions: correcting where the eyes point, not how sharply they focus.
OD and OSWhich eye is which — and why the difference between the two is worth watching.
What the conditions mean
The words a prescription implies but never prints.
MyopiaShort-sightedness — what a minus number means
HyperopiaLong-sightedness — and why young eyes hide it
AstigmatismWhy almost every eye has a little
PresbyopiaWhy reading gets harder after 40
Different in each eyeWhen the gap between your eyes matters
Is my prescription bad?What counts as mild, moderate and strong
Practical questions
The things people search for at the moment they need the paper and cannot find it.
I lost my prescriptionWho has a copy, and what to ask for
Glasses vs contact lensesWhy one prescription is not the other
Reading a contact lens RxBC, DIA, PWR and the rest
How long is it valid?Expiry by country — and why old ones still matter
How often to get testedIntervals by age and risk
Children's prescriptionsProgression, and why the trend matters most