Glasses Prescription Explained

You've been to the optician, had your eyes tested and have the prescription in your hand. You are entitled to a copy of it once you've had your test and should be given a copy without having to ask nor should the optician imply that you have to buy your glasses from them.

To most people, a prescription is just a series of numbers. Understanding what the numbers mean can help you to input the information correctly, select your lens type and consider the most suitable options.

Entering the information is very easy and is simply a matter of copying the numbers from your prescription into the appropriate boxes.

You may find boxes on our website that you don’t have on your prescription available but simply ignore them and select not required.

The basics of an eye prescription are a series of numbers for your right eye (R), and your left eye (L).

  • All numbers will be written in 0.25 increments
  • The unit of measurement for lenses is dioptres

You will sometimes see the Latin terms used for your eyes which are:

  • OS - (Oculus Sinister) for the left eye
  • OD - (Oculus Dextrus) for the right eye

Sometimes shorthand or abbreviations are used such as:

  • DV - (Distance Vision)
  • NV - (Near Vision) in place of the ‘ADD’

This image shows the various elements written on an eye prescription and what they mean:

Here is an example prescription:

Both of these are the same but are written in 2 different ways:

Here are the explanations of the different words and numbers:

SPH – (Sphere):

This box will have a ‘+’ or ‘– ‘symbol before the number.

This indicates if you are long sighted (+) and can see things far away, or short sighted (-) and can see things close up. The number refers to the power of the lens and the higher the number, the stronger the prescription lens is.

CYL – (Cylinder):

This refers to a condition called an ‘astigmatism’ and is caused by an irregular, or rugby ball shaped cornea. The higher the number, the more irregular the shape of your eye. This box may be blank on your prescription which means that you have perfectly round shaped eyes.


This number relates to the astigmatism and how much correction is needed in degrees to correct it and will be a number between 1 - 180.


This means that there is a muscle imbalance between your eyes and that they do not work well together as a pair. This prism correction will prevent double vision and correct the imbalance. Most prescriptions will not have this number.


This relates to the prism and the position of the lens.


This number relates to prescriptions which require a reading addition, hence the name ‘add’. As we age, typically around 45 years old, our eyes lose the ability to focus at a reading distance and this number is the amount of correction required to see close up. If you have a number in this box it means that you need two types of glasses for distance and reading.

Glasses prescriptions are written in many different ways. Here are some examples:

 Glasses Prescription Example


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