Get To Know Your Glasses Prescription

19th May 2022

Glasses Prescription

Nearly everyone will need prescription glasses at some point in their lives, and for many people, that time comes sooner rather than later. In the UK, it's estimated that around 70% of the population requires glasses to correct problems with their vision. And while most of us are happy to go and get our prescription from the optometrist, few of us understand what all those numbers and letters actually mean.

In this guide, we'll unpack your prescription so you can better understand your vision correction needs. We'll explain what each number and letter means, and why it's important.

What Do All Those Letters Mean?

Let's start with the basics: your prescription will always include four elements. These are Sphere (SPH), Cylinder (CYL), Axis, and Add.

Here’s a quick rundown of each one:

Sphere (SPH)

This measurement indicates how much correction you need for nearsightedness or farsightedness. If your number is positive, you're farsighted and will have trouble seeing objects that are close to you. If it's negative, you're nearsighted and will have difficulty seeing things in the distance.

The sphere is measured in Dioptres. If there is an infinity sign, Plano, or pl below the sphere, it means that the sphere measurement is zero and that you are neither long nor short-sighted.


Cylinder (CYL)

The cylinder measurement shows the amount of correction you need for astigmatism. This is when the cornea (the front surface of the eye) is curved or flattened unevenly, which can cause blurry or distorted vision.

Like the Sphere, the Cylinder is measured in Dioptres. Again, if there is an infinity sign, Plano, or pl under the CYL, it means that the Cylinder measurement is zero and you don't have astigmatism.


The Axis tells us where your astigmatism is located on the cornea and it is measured in Degrees with values ranging between 0 and 180.

An Axis figure will only be shown if there is also a CYL value present as the Axis signifies where the astigmatism is on your eye.

ADD / Addition

Add is an abbreviation for 'Reading Addition' and measures the ‘extra’ correction needed for Presbyopia. Presbyopia is a condition that usually affects people over the age of 40 and causes the eye's lens to become less flexible, making it more difficult to focus on close objects.

The Add value is only relevant if you're ordering reading glasses or multifocal lenses and will be different for each eye.


In some cases, you may also notice a value for ‘Prism’ (PR). This measures the amount of correction needed for eye turning, or Heterotropia. This is when each eye turns in a different direction and can cause double vision. If you have heterotropia, you will likely also see a base value - this tells us which way your eye is turning.

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Now for the Numbers...

The numbers shown in each box on your prescription are the measurements for each eye. The first number is always for your right eye (OD), and the second is for your left eye (OS).

OD stands for Oculus Dexter, which means ‘right eye’ in Latin.

OS stands for Oculus Sinister, which means ‘left eye’ in Latin.

Numbers range from -20.00 to +20.00, with the majority of people falling somewhere in the middle.

A plus sign (+) in front of the number means you're long-sighted, while a minus sign (-) indicates short-sight. The numbers that follow the ‘+’ or ‘-’ signs are always two decimal places. The first number indicates the Dioptre (the unit of measurement), while the second number is known as the ‘tenths’. For example, if your prescription reads +0.50 -0.75, you are long-sighted in your right eye (OD) and short-sighted in your left eye (OS).


And that's it! Now you know how to read and understand your prescription, and you can start shopping for your perfect pair of glasses.

When you're looking for glasses, you'll need to choose the right frame size, shape, and colour too. The best way to do this is to use an online glasses retailer that offers a virtual mirror feature. This way, you can try on different frames from the comfort of your own home, and find a pair that looks great.

When you've found a frame you like, simply enter your prescription details and choose your preferred lens type. Your lenses will then be custom-made and fit into your new frames, ready to be delivered straight to your door. Be sure to enter all your prescription details correctly so you can see clearly and enjoy your new glasses from the moment you put them on.

Don't forget, you can get started by browsing our collection of men's and women's glasses online. We've got something for everyone, so take a look and find your perfect pair today.

Do you have any questions about understanding your prescription? Let us know and get in touch - we're always happy to help!

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