Understanding your eye prescription


Seeing all the numbers on your glasses prescription can be quite confusing; however, it doesn't have to be if we break it down into individual sections.

SPH, or Sphere

SPH stands for spherical error and shows whether you are shortsighted (myopia) with a minus sign or longsighted (hypermetropia) with a plus sign. The higher the number, the stronger strength of lens you need to correct your eyesight.

CYL, or Cylinder

This shows how strong your astigmatism is. Astigmatism is when light is not brought to a single focus on the retina. The light is focused unevenly, often due to the eye being "rugby ball-shaped". The higher the number, the stronger the correction. If this part is left blank, then it means that you don't have astigmatism.


Axis gives us the angle that the cylindrical power in your lenses must be set at to correct your astigmatism.


Prism is short for prismatic power and is used to correct binocular vision problems, helping both your eyes work together. The number in the prism column shows the correction's strength, and the base column shows which direction the prism is acting in.


This refers to the additional correction you may need to focus at short distances and is more common over 40. The intermediate add refers to the extra strength of lenses you may need to bring a 'mid-range' distance to focus such as when viewing a computer screen. The near add is usually for close tasks such as reading. This number is added to the SPH part of your prescription to get the correct strength needed.

BVD or Back vertex distance

This is the distance between the front of your eye and the lenses used during the eye test. Altering this may impact the prescription you require in a pair of spectacles.

When you have your eye test, your optician should explain it all to you, but you can always ask them further questions if you are not quite sure. If your optician has left the appointment and you or a loved one struggles to understand your prescription and would like an explanation, please give us a call on 0800 60 50 40, and we can talk you through it.