
Your Glasses Prescription Explained
What do the numbers and words actually mean on your prescription?
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.
How to read your prescription:
An optical prescription can be split into 5 parts:
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Sphere - SPH
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Cylinder - CYL
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Axis
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Prism
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Base
1. Sphere- SPH
The SPH on your glasses prescription stands for sphere. Sphere refers to the power of your lens (measured in dioptres) to correct the degree of short or long sight that you have. Commonly, this number may differ for each eye.
This section of the prescription will have a + or - symbol before the number. This indicates if you are long-sighted (+) and
can see things in the distance or short-sighted (-) and can see things closer up. The number refers to the power of the lens and the higher the number, the stronger the prescription is. This can influence your choice of frames as the higher the prescription, the greater the curve of the lens is needed.
2. Cylinder - CYL
The CYL on your prescription stands for cylinder. This indicates the amount of lens power required to correct any astigmatism present.
Astigmatism - is caused by having a cornea that is not perfectly spherical, it is usually referred to as being a rugby ball shape. If this part of
your prescription is left blank this indicates that there is no astigmatism present. A low number such as 0.25 means that your eyes are
not quite round and a higher number such as 3.00 means that your yes are quite oval.
3. Axis
The axis number on your prescription tells your optician which direction they must position any cylindrical power in your lenses (only required if you have a CYL value). This number shows the orientation or angle in degrees from 1-180. If your prescription requires an angle 90 this means it will be set in a vertical position and 180 will be set in a horizontal position.
The higher the axis does not mean that your prescription is stronger - it just describes the position of your astigmatism.
4. Prism
A prism means that there is a muscle imbalance between your eyes and that they do not work well together as a pair. The prism correction will prevent double vision and correct the imbalance. Most prescriptions will not include a prism.
5. Base
The base simply tells the lab where to put the prism in your glasses. Most prescriptions will not have this number.
Other parts of a prescription may include:
Near or Intermediate Add: This number relates to prescriptions which require a reading or intermediate addition, hence the name 'add.' As we age, typically around 40 years old, our eyes lose the ability to focus at a reading or intermediate distance. This number is the amount of correction required to see close up or in-between such as reading or viewing the dashboard in your car.
If you have numbers in this this box it means that you have a prescription for either or both intermediate or near.
Pupillary Distance (PD): Your pupil distance is exactly what it sounds like; its the distance measured between your pupils.
This is often not written on your prescription but we recommend that you ask your optician to measure and write it down when having your eyes tested as they will likely not do it unless asked in advance.
You Must Be Given A Copy:
The General Optical Council (GOC) states that "an optician is obliged to provide you with the written prescription following the eye examination.
By law, the prescription must provide the basic results of the eye examination. You are then able to take the prescription to another supplier as you wish so that you can buy your glasses from a supplier of your choice.
Feel free to contact us if you require a copy of the glasses prescription at any stage.
