Didn’t it use to be so simple? Cover one eye, read a board a few feet away and get given some glasses. Perhaps the only jargon you’d have to be versed in was ‘short’ and ‘long’ sighted, and off on your way you went. 

But now, to the untrained, squinting eye, a prescription can look very confusing, with different numbers and abbreviated phrases, and all sorts of impenetrable lingo. If you’ve recently been to see your optician and have been told you need to wear prescription glasses, and you’re not sure what to make of your the following paperwork, then we’re here to help, with this; our IDEAL guide prescription glasses terminology.


One of the first things you may notice on your prescription are the letters ‘OD’ and ‘OS’. They are abbreviations for the Latin terms for right eye and left eye; oculus dexter and oculus sinister, respectively. This is traditional for glasses prescriptions, although some opticians may modernise it and simply use ‘RE’ and ‘LE’ for right eye and left eye; keep an eye, or both, out for each variation equally.

To add to the confusion, in some cases, you may notice ‘OU’ on your prescription. This is an abbreviation for the Latin oculus uterque, which means both eyes.


Your prescription will likely include further abbreviations and terms relating to the condition of your vision and the type of glasses you need: 

Sphere (SPH): The sphere value on your prescription refers to the amount of lens power. This is measured in dioptres, and will be prescribed to correct short or long-sightedness. If the number displayed under the sphere value has a minus sign, it means you are short-sighted. If the number has a plus sign, you are long-sighted.

Cylinder (CYL): This measurement is related to astigmatism, a common though not serious cause of blurry vision which refers to the shape of your eye’s natural curve, and indicates the amount of lens power for this type of refractive error. If there is nothing written in this column, you have no astigmatism; or it is so slight that is it not necessary to correct with prescription glasses. The cylinder power will always follow sphere power in your prescription.

Axis: The axis is defined with a number from 1 to 180, and denotes the direction of your astigmatism measured in degrees. 


As you get older, you might notice ‘Add’ on your prescription. This is the added magnifying power required for the bottom part of multifocal lenses, in order to correct presbyopia. The number in this section of your prescription is always a ‘plus’ power. It generally ranges from +0.75 to +3.00 D, with the higher number denoting a stronger prescription, and is the same for both eyes. Fortunately, it’s not a number you need to understand in detail, unless you’re a stat collector, of course.

If you’re looking advice on seasonal eye care, then check out our 5 IDEAL ways to keep your eyes healthy this winter over here.