Understanding Your Glasses Prescription


Your Glasses Prescription

Once you have had your eye examination the optometrist will give you a copy of your prescription. All opticians will present a copy of your prescription on a slightly different form but it will always contain the same information.

The form contains the precise measurements of the type of lenses that you need in order to correct your vision and help you see the clearest.

In this guide we will try to help you understand what the numbers and prefix’s mean.

SPH (sphere)

A “+” prefix indicates that you that you find it difficult to see things that are close to you. A “-” prefix indicates that you are short sighted, this means that you find it difficult to see things that are far away. The numbers can vary from a small 0.25 to a 6.00. The higher the number the stronger your prescription. This can influence the type of frame you choose as the higher the power the greater the curve of the frame.

CYL (cylinder)

Not everyone has a cyl. The amount of astigmatism (distortion of your vision) that is caused by an irregular shaped cornea. The easiest way to explain this is that having no astigmatism the eyeball is a perfect sphere, like a football. If you have astigmatism your eye is the shape of a rugby ball. The number in this part of your prescription will ascertain as to the level.


The direction of the astigmatism is measured in degrees. This tells us what angle to position your lenses in the frame.


This indicates that your eyes do not work that well together. This means that you have a muscle imbalance between your eyes. Prism lenses help to correct this to prevent double vision and headaches.


This tells us where to put the prism in your glasses.

Note: We do not include BASE or PRISM on our online form. These values are less common. If your prescription contains values for these, please contact us before placing your order.


This is your reading add. This relates to the additional correction you need to focus on things close up. You may only have additional reading. Therefore a pair of reading glasses will be required. The “ADD” can also be additional to distance vision. You can have separate glasses for distance and near vision or these can be combined with bifocal lenses or varifocals.


An “inter add” is for vision correction for everything in between distance and close up. Generally this will mean you need glasses for computer work.

We are always on hand to answer any questions you may have about your prescription via email on info@glassesonspec.co.uk

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