How to read your glasses prescription

The layout: one row per eye

Most prescriptions are a small grid with a row for each eye and a column for each value. The eye labels are often Latin abbreviations:

• OD (oculus dexter) — right eye. Sometimes written R or RE.
• OS (oculus sinister) — left eye. Sometimes L or LE.
• OU (oculus uterque) — both eyes.

SPH — sphere

SPH is the main power of the lens, in dioptres. A minus number (for example −2.25) corrects short-sightedness (myopia): you see near things clearly and far things blurred. A plus number (+1.50) corrects long-sightedness (hyperopia). Values usually move in 0.25 steps. PL, plano or 0.00 means no power in that eye.

The further the number is from zero, the stronger the prescription — and the more a thinner, higher-index lens helps.

CYL — cylinder

CYL is the power needed to correct astigmatism, where the eye focuses differently along different directions. Like SPH it can be minus or plus, in 0.25 steps. If the CYL box is empty, or the prescription says DS (dioptre sphere) or SPH only, you have no astigmatism correction in that eye.

Axis

Axis is the direction of the astigmatism correction, written in degrees from 1 to 180. It only exists when there is a CYL value — the two always travel together. An axis of 90 and an axis of 180 are completely different lenses, so copy it exactly.

ADD — addition

ADD is extra magnifying power added to the lower part of a progressive or bifocal lens for reading and close work. It is always a plus value and is usually the same for both eyes. If you only see ADD on your prescription and you want single-vision distance glasses, you don’t need it.

Prism and base (less common)

Some prescriptions include a prism value with a base direction (up, down, in or out) to correct eye alignment. It’s less common, and not every online store can make prism lenses — check before you order, or order in store.

PD — pupillary distance

PD is the distance between the centres of your pupils, in millimetres. It tells the lab where to place the optical centre of each lens. It can be a single number (for example 63) or two numbers, one per eye (31.5 / 31.5). Many prescriptions don’t include PD — your optician can measure it, and it’s quick to do at an eye test.

Worked example

Reading it: both eyes are short-sighted, the right more than the left. The right eye has astigmatism (−0.75 at 180°); the left has none. The +2.00 ADD means this person also needs reading power — so they’re a candidate for progressive lenses, which handle distance and near in one lens.

Entering it when you order online

• Copy the signs. −2.25 and +2.25 are opposite lenses. If the sign is missing on the paper, ask your optician rather than guessing.
• Right eye first. Prescriptions list OD before OS; most order forms do too.
• CYL and Axis together. If you enter one, you must enter the other.
• Use a glasses prescription. A contact-lens prescription is different (it includes base curve, diameter and the lens brand) and can’t be used to make glasses.
• Check the date. Prescriptions are generally treated as valid for a limited period, which depends on your country and your optician’s advice. If yours is old, or your vision has changed, book an eye test.

Not sure your prescription is right — or can’t find it? Many optical stores let you book an eye test online, or add the prescription after you order.

This guide explains how prescriptions are written. It isn’t medical advice — if you have questions about your eyes or your prescription, ask your optometrist or ophthalmologist.