Understanding Your Prescription

Everything you need to know about the sheet of paper you get after your eye test

Lenses lying next to a prescription form

So you’ve just had an eye test and you’ve been given a slip of paper with different symbols, letters and numbers on it. If your eye test is older than two years you will be required to get a new one before being able to buy glasses online or in store.

Don’t have a prescription but need an eye test? Check out these great deals we found for you online.

In this article, we’ll explain why you need a prescription, why they’re important, what all the numbers and symbols mean, and the different kinds of prescriptions that you can have.

A prescription is an important written document given by a qualified optometrist or suitably qualified medical practitioner, outlining a specific treatment. In the case of eyes, a prescription is given out by an optometrist or ophthalmologist and shows the health of the eye and recommends the strength of the lens you need in order to see clearly. It’s important to note that by law you should always receive a copy of your prescription. If you are not given a prescription, you should always ask for it.

Prescriptions are important because they help determine the strength of your lenses, which lenses will work best for your eyes and to some extent what frames you can wear. For example a very high short-sighted prescription would not suit a semi-rimless or metal frame as the lens required could stick out significantly.

Glasses frames lying next to a prescription form

Prescriptions for glasses are different to those for contact lenses and vice versa. This is because contact lenses sit directly on the eyeball, whereas glasses rest about one centimetre away from your eyes. A contact lenses prescription will include extra information such as: base curve, diameter, lens brand or material, and expiration date. Additionally, whereas you can go about two years between glasses prescriptions, you need a new contact lens prescription at least every year.

Single Vision Prescriptions vs. Multifocal Prescriptions

In the same way that prescriptions for glasses and contact lenses are different, so are prescriptions for single vision and multifocal prescriptions. Multifocal prescriptions are made up of two or more prescriptions (one for distance and one for reading), so you can expect your prescription to look different.

Your Prescription Explained

Ever wondered what all the symbols and numbers on your prescription mean? Our opticians explain everything, so the next time you receive yours, you’ll understand what each section means for your eyes.

+ or -

+ shows if you are long-sighted (longsightedness), – shows if you are short-sighted (shortsightedness).


Pupillary distance is the distance between your eyes measured between your pupil centre points.


Spherical number shows whether you are short- or long-sighted.


Cylinder number shows how much astigmatism you have.


Axis shows the position of the cylinder and will be between 1 and 180.


This shows if you have a muscle imbalance in your eye. To order lenses with a prism correction, please contact us.


This shows the direction of the prism in your lens.


Sometimes written as NV – this is applied to bifocal and varifocal lenses to correct presbyopia. It can also be written as near addition.

Knowing these terms means it’ll be easier for you to talk about your prescription with our opticians when ordering your glasses online.

After following steps to select your lenses and package, you’ll be given three options for sharing your prescription with us: "send prescription later", "enter new prescription", or "use saved prescription". If you’ve shopped with us before and your prescription is up to date (more on that in a second), then select "use saved prescription".

If you’re new to Glasses Direct (or have a new prescription) and have your prescription on hand, then select "enter new prescription". If you’re in need of a new prescription, select "send prescription later". This option allows you to send your prescription via photo, email, phone or post after you’ve placed your order.

Before submitting your prescription to us, you must make sure it is up to date and was given to you within the last two years. Experts advise having your eyes tested at least once every two years. Prescription older than that? Make sure you get your eyes tested soon. If you’re in need of an eye test, check out our eye test deals page where we share discounts we’ve found online.

Please note that we are unable to fulfil some prescriptions. Orders for very strong prescriptions are excluded, such as when the combined SPH and CYL is greater than +/-9.00, when the CYL is over +/-4.00, if there is more than a 5.00D difference between each eye or if the prism correction is over 4.00 in any direction. Orders for prescriptions with a combined SPH and CYL of more than +/- 8.00 can currently also only be placed over the phone.

A prescription issued by a certified optician should generally be correct, but sometimes there can still be problems with the glasses made from it.

One issue could be that the numbers haven’t been submitted correctly. You can find this out by checking the prescription you were given by the optician against the specification we have sent to you. Or maybe the numbers match but it still doesn't feel quite right. If this is the case, your prescription could still be correct, it’s just most new prescriptions take a little while to get used to. If you are still having problems after 2-3 days, contact us and one of our highly trained opticians will advise you.

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