Once your eye examination is complete and all the necessary tests have been done, the optometrist will give you a copy of your prescription. This contains the precise measurements of the type of prescription lenses that you will need in order to have the clearest, most comfortable vision.
But what do the numbers and words actually mean?
A + in the box indicates that you are long sighted which means you find it difficult to see things close to you. A – shows that you find it hard to see things that are far away without glasses. The number might be very small, like 0.25, or a large number, like 6.00. The higher the number, the stronger the prescription lenses required. This can influence your choice of frames. The higher the prescription, the greater the curve of the lens needed.
The amount of astigmatism (visual distortion) that is caused by an irregularly shaped cornea. If this box is empty, it means that there is no astigmatism and your eyes are perfectly spherical, like a football. If there is a low number, like 0.25, it means that your eyes are nearly round but not quite. A higher number, like 3.00 shows that your eyes are quite oval in shape.
The direction of the astigmatism, measured in degrees. The number is not related to how well you can see but it helps the lab know what angle to position your lenses in the frame.
This usually indicates that your eyes do not work well as a pair. If there is muscle imbalance between your eyes, prism lenses will provide the correction you need and help prevent double vision or headaches.
The base simply tells the lab where to put the prism in your glasses.
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 distances. If a measurement is shown in this section, it means you have different prescriptions for distance and reading. Bifocal or varifocal lenses may be needed.