Prescription Explained


There’s a lot of numbers and letters on an eye test prescription, so to help you understand the jargon we’ve put a quick guide below.

SPH - Sphere

This tells you the power of the lens needed to correct your vision. It will have either a + or a - before the number.

A minus sign ‘-’ indicates that you are short-sighted. A plus sign ‘+’ indicates that you’re long-sighted.

CYL - Cylinder

If you have an astigmatism, you will have a number under CYL. This tells you how strong your astigmatism is and how much correction is needed. The higher the number (e.g. above 4), the stronger the astigmatism. CYLs or Cylinders help to correct astigmatism by providing more power over one area of the lens.

Find out more about astigmatism here.


The axis will indicate where the CYL needs to be positioned on the lens to correct the astigmatism.

Near Add

If you have a number here on your prescription you will be wearing Varifocal lenses. It is the amount of correction that is needed on your distance prescription to give you your reading prescription.

Intermediate Add

Similar to the Near Vision Add, this is the amount of correction needed on your distance prescription to give you your intermediate prescription (for looking at something at mid-range, such as a computer screen).


Prisms are prescribed if you suffer from double vision. They can help the eyes work together and create one image instead of two.


The base is simply where the prism needs to be positioned in the lens when it is being made.



PD, or Pupillary Distance, is the distance between the centre of your pupils. We need this measurement when we make your glasses, to ensure you are looking through the clearest part of the lens.

If you don’t have a copy of your PD measurement from your opticians, we have explained below how to measure it yourself.

You will need a ruler and a mirror.

  1. Stand approximately 30cm away from the mirror.
  2. Hold the ruler just above your eyes, resting on your eyebrows.
  3. Closing your right eye, line the 0mm part of the ruler up with the centre of your left pupil.
  4. Keeping the ruler still, open your right eye and close your left eye.
  5. Look at the measurement that lines up with the middle of your right pupil. This is your pupillary distance measurement.