How to read your glasses prescription (SPH, CYL, AXIS and more)

By The STOTTS. Clinical Team 5 min read Published 22 August 2026 Reviewed 22 August 2026 Reviewed by Phil Houston, Optometrist, BSc MCOptom

A glasses prescription can look like a row of code — a grid of pluses, minuses and abbreviations. In fact each one describes something simple about how your eyes focus. Here is what the numbers mean, so you can make sense of your own.

Right eye, left eye

Your prescription is set out in two rows, one for each eye. You will see R (or OD, for the Latin oculus dexter) for the right eye, and L (or OS, oculus sinister) for the left. The two eyes often differ, which is completely normal.

SPH — the main lens power

The Sphere is the core of the prescription — how much focusing correction each eye needs. A minus (−) figure means you are short-sighted (distance is blurry), and a plus (+) figure means you are long-sighted. The bigger the number, the stronger the lens. A reading of 0.00 or “Plano” simply means no correction is needed in that respect.

CYL and AXIS — astigmatism

These two go together and describe astigmatism, where the eye is shaped a little more like a rugby ball than a football. CYL (Cylinder) is the amount of astigmatism, and AXIS is a number from 1 to 180 that tells the lab which way it is oriented. Plenty of people have some astigmatism; it is easily corrected.

ADD — your reading boost

If there is a figure under ADD (addition), it is the extra magnifying power for close work, added to the bottom of the lens in reading, bifocal or varifocal glasses. It usually appears from your forties onwards, as focusing up close becomes harder.

Other things you might see

• PRISM and BASE — occasional additions that help the eyes work together
• PD (pupillary distance) — the gap between your pupils, used to centre the lenses correctly
• A date — a glasses prescription is generally considered valid for about two years

One important note: it is not a contact lens prescription

A glasses prescription cannot be used to order contact lenses. Because lenses sit directly on the eye, they need a separate contact lens fitting that also specifies the lens type, base curve and diameter. If you would like to try lenses, a quick fitting is the starting point.

Once you know that minus means short-sighted, cylinder and axis mean astigmatism, and ADD means reading help, your prescription stops being code and starts making sense.