How To Read Your Prescription
The abbreviations mentioned in the prescription chart are explained below:
The sphere measurement determines the strength of your lens prescription . The measurements are quite simple if there is a + (plus) in this box it means that you are long sighted (difficult to see things up close, easier to see things at a distance) and if it is a - (minus) you are short sighted (easier to see things up close, difficult to see things further away). This number can range anywhere from +/- 0.25 to more than +/-20.00 and this will determine the strength of your prescription which can influence both your lens and frame choices.
The cylindrical measurement is based on the shape of your eye. This is referred to as the astigmatism. How elliptical your eye is determines the amount of astigmatism. If there is no number, a zero or an infinity symbol in this box then it means your eye is perfectly spherical like a football. Low measurements mean your eye is almost spherical but not quite, while higher numbers indicate more of an oval shaped eye, like a rugby ball.
The axis measurement is the direction or angle of your astigmatism. It is measured in degrees. It is not related to how well you can see but does let us know how to position the lens in your frame.
Inter-Add (Intermediate Addition)
If you are over 50, the power required to view the computer at arms length may be different to the power required to read a book closer up. This power will be described as the INTER-ADD on your prescription. Specifically for computer use you may need Digital Protection Lenses.
Near-Add (Near Addition)
If you are over 45, there may be a number where it says ADD. This is your reading addition and relates to the amount of additional correction needed to focus at close range. If a measurement is shown in this section, it means you have different prescriptions for distance and reading. Varifocal lenses may be needed.
A prism is a lens treatment that is added on to your spectacle prescription to help your eyes focus better together or reduce double vision.
The direction of the prism is called the base. This will be mentioned on your prescription next to the prism.
Pupillary Distance (PD)
Pupillary Distance or PD is the distance between the two pupils.