Understanding The Numbers

How do I read the numbers on the results of my eye examination?

Have you ever come out of an eye test and wondered what all the numbers and abbreviations mean? Here is a quick guide to help you better understand your prescription.


There are two ways in which your prescription can be presented, either in a table as shown below or in a line such as -1.00/-0.25 x 128. In the linear form the first number is the Sph, the second is the Cyl and the third is the Axis



Your prescription is recorded in dioptre, the unit of the power your eye need to correct your vision.


This stands for ‘spherical’ and is a measure of how long or short sighted you are. The further the number is from zero the worse your vision can be and the stronger the correction you require to focus your eyes. A plus (+) means you are long sighted and a minus (-) indicates you are short sighted.  For example, the right eye here has one dioptre of short sightedness.


This is short for cylinder, this is the measure of the astigmatism of the eye. Astigmatism is when the eye is shaped more like a rugby ball rather than a football. Again, the larger the number the more astigmatism you have. The left eye here has one dioptre of astigmatism.


This is measured in degrees and it is the orientation of the astigmatism. The left eye has one dioptre of astigmatism at 150 degrees.


Something that can be a worry for some people is how the numbers change each time they go for an eye test. Both spherical and cylinder measurements change in 0.25 steps. Therefore, someone’s version may go from -0.50 to -0.75, and you may worry that it is a big change, but it is only one step and you may not even notice that there has been a change in your vision.

Routinely you should have an eye test every two years (unless your optometrist advises it more regularly), however if you notice a change in your vision you can go sooner for advice.

If you’re concerned about a significant change in your eyesight make an appointment with your local optometrist. If you would like to arrange an appointment with us at Cathedral Eye Clinic send us a message via Live Chat, fill in the form below, or you can call us on 028 9032 2020 and a member of our Patient Care Team will help arrange your booking.

 by Haley Murphy

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