How do I read my glasses prescription?



After an eye exam, your optician will give you a copy of your prescription. By UK law, they are required to give this information to you and if they haven’t, you should ask for it. Once you are given your prescription, it can be difficult to understand what the words and numbers mean. We've broken down the different parts of your prescription to make things easier.

What do the symbols on my prescription mean?

OS and OD

When you look at your eyeglasses prescription, you will see numbers written under the headings of OS and OD. OS is a Latin abbreviation for oculus sinister which means left eye, whilst OD is for oculus dextrus which means right eye.

The further away from zero the number on your prescription, the more correction you will need for your eyesight.

+ or -

The plus symbol (+) means you are long-sighted. The minus symbol (-) means you are short-sighted.

Sphere (SPH)

The sphere number indicates the lens power, or to what degree you are short or long-sighted. You will find the + or - symbol here to indicate this.

Plano or ∞

Plano, sometimes referred to as pl or the infinity symbol, means that no visual correction is required.

You may also find these under the sphere section.


PD stands for Pupillary distance pd and measures the distance between your eyes, from the centre point of one pupil to the other.

In most cases your optician will not add this to your prescription, however it is important to know if you are purchasing prescription lenses online, especially if you have a high-strength prescription as it is important to have lenses that accurately centred.

Cylinder (CLY)

CLY stands for cylinder power which refers to how mild or severe your astigmatism is. Astigmatism is when the front part of your eye is shaped more like a rugby ball than a circle. Your prescription will include this if you need to correct astigmatism.


Axis measures the cylinder of your eye and goes from 1 to 180. If you do not have astigmatism, you won’t see cyl and axis on your prescription.

DS (in cyl column)

DS stands for diopter sphere, which means a spherical correction. If this is left blank, then there is no astigmatism that requires correcting.


Also written as near addition or NV – indicates that a prescription for reading or focusing at close distances is required.

You'll usually find this on your prescription if you are over 40 and indicates correction for presbyopia. It is applied to bifocal or progressive (varifocal) lenses and will mean that you have a different prescription for distance vision and reading.


The prismatic power is shown here and is most commonly written in fractions (e.g 1 ½)

It is prescribed if you have difficulty focusing on something with both of your eyes at the same time and means that you have a muscle imbalance in your eye.

The ability to use both your eyes to see a single image is also known as Binocular Vision.

A prismatic power may also be prescribed if you have double vision and issues with looking in different directions.


The base refers to the direction of the prism in the lenses and is shown under abbreviations. BU stands for Base Up, BD is Base Down, BI is Base In and BO is Base Out.


Balance or bal refers to the prescription in that particular eye and means that no values are needed for that eye. The lens for this eye is made to the same weight so that the glasses feel balanced when on the face.


VA stands for visual acuity and measures how clearly you can see the letters and numbers on a standardised testing chart from a set distance away. For the UK the set distance is 6 metres. In the US they test your visual acuity at 20 feet which is where the term 20/20 vision derived from.

Here is a comparison of different prescriptions from opticians:

The examples below show various prescriptions from opticians alongside examples of how these prescriptions should look when entered on our website.

It would be entered on our website as follows:

Full Prescription

Please note: The ADD value (Near-ADD and Inter-ADD) won't always be mentioned on your prescription, in this case please leave it blank when you enter your prescription on our website.
It would be entered on our website as follows:

Specsavers Prescription

Please note: You do not need to enter the BVD value if it is mentioned on your prescription.
Vision Express
It would be entered on our website as follows:

Vision Express Prescription

Please note: If you would like to order glasses for distance you do not need to enter the ADD value.
It would be entered on our website as follows:

Boots Prescription

Please note: You do not need to enter the Distance acuity and Near acuity if it is mentioned on your prescription.
It would be entered on our website as follows:

Hospital Prescription

It would be entered on our website as follows:

NHS Prescription

NHS Scotland
It would be entered on our website as follows:

NHS Scotland Prescription

Please note: The cylinder (CYL) value is written in a plus (+) format, make sure to select plus (+) instead of minus (-).
David Clulow
It would be entered on our website as follows:

NHS Scotland Prescription

Please note: If you would like to order glasses for distance you do not need to enter the ADD value.

Can I use my glasses prescription for contact lenses?

The prescription you are given for your glasses and the one you are given for your contact lenses are different. They should not be used interchangeably as contact lenses sit on the surface of the eye and glasses are flatter and sit further away from the face.

If you’re looking for help, check our guide on reading your contact lens prescription.

What is the difference between single vision and multifocal prescriptions?

Single vision means that your lenses have one single prescription power throughout the whole lens. Single vision lenses are used for correcting near sightedness and short sightedness. Multifocal lenses have multiple prescriptions within the same lens, this allows the user to see at multiple distances without needing several pairs of glasses. Types of multifocal lenses include bifocal, trifocal and varifocal lenses.

What types of lenses are there?

Depending on how your vision needs to be corrected, you will be prescribed a certain type of lens.

Single vision

A single vision lens means that the corrective power is the same all over the lens; this is the most commonly prescribed lens. People who use their glasses primarily for reading and driving tend to have single vision lenses.

A single vision lens can be used for all distances and various activities, this includes reading (near), driving (far) and computer work (intermediate or an arm's length)..


When you need one prescription for distant objects and another one for seeing close objects, bifocal glasses are an alternative to carrying around two pairs of glasses. Bifocal glasses have two sections on the lens divided by a visible line; the top section is larger and is used for distance; the bottom section is for reading or viewing objects close to you.

Progressive vision

Progressive lenses have three sections, distance at the top, intermediate in the middle and near vision at the bottom. Unlike bifocal lenses, progressive lenses have no visible lines between the sections and the power of the lens moves seamlessly from one section to the next.

How do I submit my glasses prescription on FGC?

After having chosen your lens type, you can then enter your prescription. Make sure your prescription is valid and has been taken within the last two years. If your prescription is older than two years then you will need to book an eye test to get a new one. If you've ordered from us before then your prescription will already be saved.

Does FGC accommodate lenses for all prescriptions?

We do a wide variety of prescriptions; however, we are unable to do very strong or very high prescriptions. The combined sphere and cylinder (cyl) values cannot be greater than a minus 8 or a plus 6, with the cyl value not being over plus 2 or minus 2.

You should now have a better understanding of what your eyeglass prescription means which will help you select the right optical glasses for you and your visual requirements.