Smart Specs Check

How to read a glasses prescription: SPH, CYL, AXIS and ADD

A UK glasses prescription gives, for each eye, a sphere (SPH) for long or short sight, and a cylinder (CYL) and axis for astigmatism if you have it. Some cards also give an addition (ADD) for reading. Keep the plus or minus sign on every number.

A worked example

This card is made up for illustration. Your own card may use different layouts, and some boxes may be blank.

EyeSPHCYLAXISADDPRISM
R−2.00−0.5090+2.00—
L−1.75−0.7585+2.00—

What each column means

Short sight and long sight: the plus and minus signs

In the SPH column, a minus sign means short sight (myopia), and a plus sign means long sight (hypermetropia). The NHS describes short sight as a condition where you cannot see objects far away clearly. Keep the sign when you copy a number anywhere: −2.00 and +2.00 are opposite corrections.

Astigmatism: what CYL and AXIS show

The NHS says astigmatism means your eye is shaped more like a rugby ball than a football. A CYL value with an AXIS shows the lens corrects astigmatism, with the AXIS giving the angle. A DS entry in place of a cylinder means no astigmatism correction is needed. For how cylinder limits apply to each model, see cylinder limits by model.

Reading additions (varifocals and reading lenses)

If your card has an ADD figure, it is the extra power for near or intermediate work. Whether a model takes varifocal (progressive) lenses is a separate question, covered on the varifocal page.

PD: pupillary distance

PD is the distance between your pupils. The College of Optometrists says it is not part of the prescription, and the NHS says an optometrist is not required by law to include it. It is measured during dispensing, so the dispensing optician who fits your glasses is the person to ask. You will usually not find it on your card.

Getting your prescription after a sight test

Under section 26 of the Opticians Act 1989, the person who tests your sight must give you, immediately after the test, either a signed written prescription or a signed statement that you do not need glasses. The NHS says the optometrist is legally required to give you your prescription, and that you should never feel obliged to buy glasses from the practice that tested you.

How often to have a sight test

The NHS recommends a sight test every two years for adults, and more often if an optometrist advises it.

A glasses prescription is not a contact lens specification

Powered contact lenses must not be supplied without a valid contact lens specification, according to the College of Optometrists. A glasses prescription is a different document, so it cannot be used to order contact lenses.

Using your prescription with smart glasses

Enter the SPH, CYL and AXIS for each eye in the checker. It compares them with published lens ranges and says whether they are inside or outside a range. It does not recommend a model. You can also see how strong a prescription each model takes, and which models take varifocal lenses.

This tool compares your prescription with published manufacturer or lens-provider ranges. It is not optical advice and does not replace a dispensing optician. Use a current prescription and ask your dispensing practitioner to confirm the applicable prescription-age and supervision requirements. In the UK, prescription spectacles for anyone under 16, or registered sight impaired or severely sight impaired, must be supplied by or under the supervision of a registered practitioner.

Sources

All sources were read on 13 November 2026.