Understanding your prescription
What do the letters, numbers and symbols on my prescription mean?
Apart from your name and date of birth, you will notice that there are quite a few letters, numbers and symbols on your prescription. This is what they all mean:
‘+’ or ‘-‘
‘+’ – Shows if you are long sighted (longsightedness)
‘-‘ – Shows if you are short sighted (shortsightedness)
SPH or Spherical number
This shows how strong the correction needs to be. A ‘-‘ symbol above the number indicates shortsightedness whereas a ‘+’ symbol indicates longsightedness. Other symbols that can be found in this section are the infinity symbol (which looks like a sideways eight) or the word Plano (or Pl), which are the equivalent of ‘zero’ and are used when no sight correction is required. Another common term that can be found on prescriptions is V/A (or visual acuity) which measures the standard of vision when corrected.
CYL or Cylinder number
This shows how much astigmatism you have and the number can be negative or positive. Astigmatism is when the front part of your eye is shaped more like a rugby ball than a regular circle. If you don’t have an astigmatism, there will be no figures written in the cylinder and axis boxes.
AXIS
This shows the position of the cylinder. It will be between 1 and 180.
PD or Pupillary distance
This is the distance between your eyes measured between your pupil centre points. Usually, the optician will not add this to your prescription, so you should ask for it as it’s important for those with high-strength prescriptions to have lenses that are centred more accurately. 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.
ADD
This will indicate if you need a prescription for reading and is applied to bifocal and varifocal lenses to correct presbyopia. You may also have an Inter Add for computers or other tasks like reading music on a stand.
PRISM
This shows if you have a muscle imbalance in your eye. It’s less common to see this box filled in as it’s fairly rare. The prism is usually written in fractions (for example 1 ½).
BASE
This shows the direction of the prism in your lens, for example IN, OUT, UP or DOWN. This is fairly uncommon so the boxes are normally empty.
You can read more about different types of prescriptions here.
Common layouts of prescriptions
Below are examples of prescriptions. The first set are standard - look through these to get a feel. It’s mostly handwritten prescriptions that cause problems but typed ones are generally easier to understand. For each prescription, we also included how it would appear when adding it to our website.
At the end of the page are examples of unusual cases you may encounter, with instructions for what to do. Skip straight to the more unusual items.
This is a standard NHS prescription:
It would be written as follows:
NHS Scotland
- Here the signs have been written ABOVE the numbers - they are still just standard +/- signs.
- It can be hard to tell where one number ends and the next one begins. It helps to know that sphere and cylinder will always be in the format (x)x.yy, with x being a number from 0 to 10 and yy being either 00, 25, 50 or 75. Axis is always a number between 1 and 180.
It would be written as follows (you can click “My prescription is more complex than this…” to expand the menu):
Boots
It would be written as follows:
Specsavers
It would be written as follows:
Vision Express
It would be written as follows:
More unusual figures
If you need a prism for one or both eyes, it will look similar to this:
We can provide lenses with a prism correction, but you’ll need to contact us to discuss this.
Sometimes figures like this appear on your prescription. These are not needed to make your lenses.
Some prescriptions have this figure, which looks like a sideways 8. This means ‘infinity’. And you should select ‘infinity’ from the list.
This prescription also has some figures scrawled underneath - these are additions for both intermediate and near distances. Even though it’s a single figure, it applies to both eyes.
To enter this, you’ll need to use the “My prescription is more complex than this…” link to show the more advanced prescription area.
Sometimes opticians write ‘DS’ in the CYL column. This simply means there is no astigmatism, and you can enter either nothing (leave the field blank) or select the phrase DS in the drop down.
