Your prescription

What it means

On your prescription, as well as some basic details such as your name and date of birth, there will usually be a table that shows your prescription.

What the numbers mean

  1. The first number is called the ‘spherical number’, and this will show whether you are short sighted (-) or long sighted (+) in each eye. A higher number means a stronger prescription.

  2. If you have astigmatism (when the front part of the eye - the cornea - has the shape of a rugby ball instead of a regular circle), there will be a second and third number. The second number is the ‘cylinder number’, which can be negative or positive and measures the amount of astigmatism you have. If you don't have an astigmatism, there will be no figures written in the cylinder and axis boxes.

  3. The third number is the ‘axis number’, which will be between 1 and 180. The axis number indicates the position of the cylinder.

  4. Sometimes, you may have a muscle imbalance in your eye, so your optician will prescribe a prism and a prism base. The prism is usually written in fractions (for example 1 ½) and the prism base shows the direction of the prism in the lens (for example, IN, OUT, UP or DOWN). This is fairly uncommon so the boxes are normally empty.

Some prescriptions might also have a 'Reading addition' (Add) number, which indicates the change in power needed to correct Presbyopia (ie when you need a different requirement for reading or close work tasks, you may also have an Inter Add for computers or tasks like reading music on a stand).

Other symbols that can be found in the Sphere (SPH) box of the prescription are the infinity symbol (∞) or the word Plano (or Pl), which are equivalent of 'zero'. They are used when no sight correction is required, this means that you are neither long nor short sighted. Another common term that can be found on prescriptions is V/A (or visual acuity) which measures the standard of vision when corrected.

You should also ask the optician for your pupillary distance (PD). Your PD is the distance between your eyes, measured between the centre of your pupils. If you have a high-strength prescription, it is more important that you lenses are centred more accurately. Usually, the optician will not add this to your prescription, so you should ask for it. To ask for your PD, you can tell your optician that you will be purchasing an item they do not stock, such as prescription goggles online.

Now you are ready to look for the perfect frames, wherever that might be. Remember, you do not have to buy frames from where you had your eyes tested.