Understanding your prescription

Prescriptions can be confusing, here’s our quick guide to help you understand your prescription.

What do all of the symbols and numbers on your prescription mean?



A “-” prefix usually indicates that you are short sighted, this means that you find it difficult to see things that are far away.

A “+” prefix usually indicates that you that you find it difficult to see things that are close to you.


You are likely to see the abbreviated terms OD, OS and OU. OD refers to Oculus Dexter while OS represents Oculus Sinister. They are Latin words that mean right eye and left eye. OU refers to Oculus Uterque, it stands for both eyes. These are the traditional abbreviations that doctors use when writing prescriptions for eyeglasses. However, some eye doctors prefer to use modernized prescriptions. R stands for right eye while L stands for the left eye.


Sphere (SPH) – stands for the spherical error and shows whether you are shortsighted (with a minus sign), or longsighted (with a plus sign). If your prescription has the word Plano, PI, or an infinity sign, it means that you do not have distance problems. You may, however, have astigmatism.


Cylinder (CYL) – Cylinder represents the amount of lens power you need for astigmatism. You may not have anything indicated in this column if you do not have an astigmatism. The value may be a plus or a minus, and in most cases, the value will be between +/-0.25 to +/-4.00.



Axis Axis shows the position of the cylinder and will be between 1 to 180. An axis of 90 represents the vertical position while 180 represents the horizontal position. The numbers describe the position of astigmatism and the Axis will be present if there is a Cyl value.



Prism – A prism specifies any vision displacement, like double vision. It may correct conditions including particular eye disorders and conditions that need the image in focus to change its position. It is measured in Prism Dioptres and they come with directions such as UP, DOWN, IN, and OUT.



Base Specifies in what direction the prism is to be set.



Addition (ADD) – Is short for Reading Addition (Sometimes referred to as SEG POWER as well). It is an additional plus power in the lower portion of a multifocal lens (progressive or varifocal) that is required for near vision.



Pupillary Distance (PD) – PD is the distance from the center of the pupil in one eye to the center of the pupil in the other eye. The PD may be written with the Pupillary Distance listed for each eye respectively, for example RE: 30,5 LE: 31,5, or as one measurement PD: 63.


Other figures

DS – This means “Dioptre Sphere”, and means that the Cylinder value is zero. The Axis value will also be blank.

Plano, Infinity – This means that there is no correction required or 0.00.

VA (Visual Acuity) and BVD (Back Vertex Distance) –  These figures may appear on your prescription in addition to the standard values. You do not need to enter any of these additional values to place an order.

Common prescription layouts

The prescriptions shown below are an example of some of the most commonly used formats. You may have a printout from your Opticician, an NHS GOS claim form with your prescription or both.

NHS GOS claim forms

The prescription above would be entered on the website as follows –

Distance lenses:

For distance lenses, we would only require the values from the horizontal distance row on a GOS claim form.

Reading and Varifocal/Progressive lenses:

For reading lenses, we need your distance values and near ADD (Near Addition). The near ADD (Near Addition) is not always written on a NHS GOS claim form but if there are two rows (Distance and Near) we can work out what your ADD value is by taking the values from both the Distance and Near rows as shown below. If you have figures in the Distance and Near rows please click on the ”PRESCRIPTION LOOKS DIFFERENT? Click here to change the layout.” option and then select ‘My prescription has two completed rows of figures or is printed on an NHS GOS form.‘ The layout will alter allowing you to enter both Distance and Near rows.

Note: If your ADD value is written and says INTER ADD (Intermediate Addition) this may be different from your near ADD. We are not able to calculate your INTER ADD (Intermediate Addition).

Boots Opticians

Distance lenses:

Reading and Varifocal/Progressive lenses:

Vision Express

Distance lenses:

Reading and Varifocal/Progressive lenses: