How to Read Your Eye Prescription

📅 20 Aug 2026 ⏱ 5 min read 👁 Eye Dive Optical, Karnal

Your optometrist hands you a slip of paper covered in abbreviations and numbers. Most people fold it up, put it in their wallet, and have no idea what any of it means. This guide fixes that.

OD and OS — Which Eye Is Which?

Every prescription starts by identifying your eyes using Latin abbreviations:

OD (Oculus Dexter) — your right eye
OS (Oculus Sinister) — your left eye
OU (Oculus Uterque) — both eyes together (used for ADD power)

Some prescriptions use R and L instead — same meaning, simpler notation.

The Main Numbers — SPH, CYL, Axis

Term	Full Name	What It Means
SPH	Sphere	Your main correction. Negative (−) = short-sighted. Positive (+) = long-sighted. "Plano" or 0.00 = no correction needed.
CYL	Cylinder	Corrects astigmatism. If this is blank or 0.00, you have no astigmatism. Usually negative.
Axis	Axis	The direction of your astigmatism, measured in degrees from 1 to 180. Only present if you have a CYL value.
ADD	Addition	Extra magnification for reading — only for people 40+ who need bifocal or progressive lenses.
PD	Pupillary Distance	The distance between your pupils in millimetres. Essential for lens centring.

Reading the Numbers

Powers are written in steps of 0.25. A typical prescription looks like this:

    OD (Right): −1.50 / −0.75 × 180

    OS (Left): −1.25 / −0.50 × 165

    This means: right eye needs −1.50 sphere, −0.75 cylinder at axis 180°. Left eye needs −1.25 sphere, −0.50 cylinder at axis 165°.

What the Sign Means

Minus (−) — myopia / short-sightedness. You see near clearly, not far.
Plus (+) — hyperopia / long-sightedness. You strain to see near objects.
Higher numbers — stronger prescription. −5.00 is stronger than −1.00.

Astigmatism — CYL and Axis Together

Astigmatism means your eye is shaped more like a rugby ball than a football. The CYL value corrects the distortion. The Axis tells the lens where to apply that correction. You always need both — a CYL without an Axis (or vice versa) is incomplete.

ADD Power — For Reading After 40

As we age, the eye's lens stiffens and loses its ability to focus up close. ADD power compensates for this. It appears in bifocal and progressive prescriptions. The same ADD is typically prescribed for both eyes — usually between +1.00 and +3.00.

    Quick tip: If your prescription has an ADD value, ask us about progressive lenses. They give you clear vision at all distances — no bifocal line, no switching between two pairs.
  

Prescription Validity

Eye prescriptions are typically valid for one year for adults, and six months for children under 16 (eyes change faster in younger patients). If yours has expired, an eye test takes about 20–30 minutes at our store — no appointment needed.

Get Your Prescription Anytime

Every visit to Eye Dive is recorded. If you've lost your prescription card, you can retrieve your full power history online using your registered mobile number — no paperwork, no waiting.

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Eye Dive Optical

Shop No. 8-9, Kunjpura Road, Karnal · Serving Karnal since 1989