There are several basic terms you will come across our website when ordering prescription lenses. Here’s a short description of all of them below:
Sphere (SPH) stands for the prescription power in the dioptres. Sphere indicates how much magnifying power your lenses must provide to correct your vision.Plus powers (+) indicate you are long-sighted (unable to see things close up). Minus powers indicate you are short sighted (unable to see things in the far).
Cylinder (CYL) is the amount of lens power needed to correct your astigmatism. Astigmatism is a condition where your cornea is irregularly shaped (sometimes referred to as rugby ball shaped eyes) causing blurred vision. If no cylinder power is indicated in your eyeglass prescription, you have no astigmatism and you should leave those boxes blank when ordering.
Axis indicates the direction of your astigmatism. If no cylinder power is indicated in your eyeglass prescription, you have no astigmatism and you should leave those boxes blank when ordering.
Near Add, short for “nearaddition”, is the additional correction required for reading, this can be used to make either reading glasses, bifocal glasses or Varifocal glasses. This number is an indication of how much extra power is required ‘on top’ of the distance prescription for near or intermediate glasses.
Prism is used to correct eye alignment issues. Prism value will also be followed by a directional value – i.e. Base down or base up. Only a small amount of prescriptions will require a prism.
Pupillary distance (PD) is the distance between the centres of your pupils, generally measured in millimetres(mm). Pupillary distance is used to align lenses over the centre of your pupils for perfect clarity.