The sphere value or power indicates the strength of your glasses. You can find this on your current prescription abbreviated to S or SPH. If you are long-sighted, the number will be preceded by a plus symbol (+). If you are short-sighted the number will be preceded by a minus symbol (-). Please check that you have entered the correct symbol when placing your order. If no plus or minus symbol is indicated for the sphere power on your prescription, you should generally read this as a plus (+).
Cylinder (CYL) - Only used in cases of astigmatism.
The cylinder power indicates an astigmatism of the cornea. You can find this value on your current prescription abbreviated to CYL. Please take care with these signs on your order. Please check that you have entered the correct symbol when placing your order. If no plus or minus symbol is indicated for the cylinder power on your prescription, you should generally read this as a plus (+).
Axis (A / ACH) - Only used in cases of astigmatism.
The axis value is given in degrees and describes how the lens is positioned in your glasses, in order to correct an astigmatism. The axis value ensures that the lenses are perfectly aligned in your glasses. You can find this value on your current prescription abbreviated to A or ACH. The axis number is always between 0° and 180°.
Addition (ADD) – Only used for varifocals and reading glasses
The addition value, also known as near addition, is only used for varifocals and reading glasses. You can find this value on your current prescription abbreviated to ADD. The addition number is the same for both eyes and you will often see it written only once on your prescription.
The pupillary distance measures the space between the centre point of each of your pupils to the middle of the bridge of your nose, and is given in millimetres. In most cases the pupillary distance can be found on your prescription abbreviated to PD. You will usually have a separate number for each eye. The pupillary distance number is generally between 25 and 38 mm.
In some cases the pupillary distance is given as a single number and generally lies between 50 and 76 mm. When ordering your glasses divide this number by two, and use the resulting number for both your right and left eyes (ie. a pupillary distance of 60 mm should be entered on your order as 30 mm for the right eye and 30 mm for the left eye).
Don’t worry if you don’t know your pupillary distance. You can use our guide Finding your PD or simply leave the PD field on your order blank and our opticians will contact you directly by email once you have placed your order.
Still have questions on understanding your prescription or the PD? Our opticians are here to help:
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