THE ANATOMY OF A PRESCRIPTION

	SPH	CYL	AXIS	ADD
OD	−2.25	−0.75	175	+0.75
OS	−2.75	−0.50	12	+0.75

PD 62 mm · Progressive lenses

Decode your own prescription

Type the values from your paper. We translate them into plain language — free, instant, nothing stored.

	Sphere (SPH)	Cylinder (CYL)	Axis	Add
ODright
OSleft

On your prescription, SPH may be written as Esf/Sph, CYL as Cil, axis as Eje/×. OS is sometimes OI.

OD and OS — which eye is which

OD (oculus dexter) is your right eye; OS (oculus sinister, sometimes OI in Spanish) is your left. They're almost never identical — and how the difference evolves over the years is one of the most useful things a lifelong record shows. The full OD / OS / OU guide →

The five numbers

SPH — sphere

The main power of the lens, in diopters. A minus number corrects short-sightedness (myopia): distance is blurry, near is sharp. A plus number corrects long-sightedness (hyperopia). The further from zero, the stronger the lens. What SPH means →

CYL — cylinder

Your astigmatism: the front of the eye is slightly oval instead of round, so it focuses unevenly. Most people have a little. Under about −0.75 it's mild; beyond −1.50 uncorrected lines can look stretched or doubled. What CYL means →

AXIS

The direction, from 1° to 180°, along which the cylinder correction is placed. It's a position, not a strength — an axis of 175° isn't "more" than 12°, just differently oriented. What AXIS means →

ADD — near addition

Extra plus power for close work, used in reading, bifocal and progressive lenses. It appears when presbyopia arrives — the normal stiffening of the eye's focusing lens, typically from the mid-forties. What ADD means →

PD — pupillary distance

The distance between your pupils in millimetres. Labs need it to center the lenses in front of your eyes. It's often missing from the paper — worth asking for and keeping in your record. What PD means →

Prism and base

On a minority of prescriptions, correcting where the eyes point rather than how sharply they focus. Written as an amount in prism dioptres plus a base direction (BI, BO, BU, BD). What prism means →

Minus or plus cylinder? The same correction can be written two mathematically-equivalent ways. European optometry usually writes minus cylinder; some ophthalmology notation uses plus. RefraCard stores one normalized form and shows whichever convention you prefer — the values never change, only the notation.

Prescription vs refraction

The machine's measurement (the objective refraction) and what you're actually prescribed can legitimately differ — clinicians often soften a correction for comfort and adaptation. That's why your RefraCard keeps both, when you have them: the prescription up front, the objective refraction one tap behind it.

A girl seated behind a digital automated refractor while the optometrist steps her through the lenses — **The measurement, and the prescription.** Behind the lenses is the objective refraction — what the instruments read. What you are handed afterwards is a clinical judgement built on top of it, often softened a little for comfort. Both are worth keeping, and they are not always the same numbers.

Why keep the history

A mother wearing glasses reading a book with her young daughter under a warm lamp — A card each for you and your children, managed from one account.

One prescription is a snapshot. Ten are a story.

Whether your myopia is stable or creeping, when presbyopia arrived, whether your astigmatism axis is drifting — the context every new optometrist wishes they had, and, for children, the progression curve that myopia management decisions depend on.

So the paper from a shop that closed in 2019 is still there when someone finally asks what your eyes were doing back then.

Decode your own prescription Start your record

What the conditions mean

The words your prescription implies but never prints — what each one actually is, and which of them are worth watching over time.

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 actually 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