Your contact lens prescription is on the side of your contact lens box. You can also ask your optometrist, who has it on record, and you are given a copy when you have a contact lens fitting or a check-up. A contact lens prescription is not the same as a glasses prescription: besides the power, it gives the curve, the diameter and the brand of the lens, and the power often differs from your glasses, because a contact lens sits on the eye.
How to read it
The power of your prescription
- Power or sphere (SPH, in dioptres, D). The main power of the lens. A minus (-) sign means short-sighted, and a plus (+) sign means long-sighted.
- Cylinder (CYL). The extra power that corrects astigmatism. If this space is empty, there is no astigmatism to correct, and you only have a sphere power.
- Axis (AX). A number from 0 to 180 degrees. It is the direction of the cylinder power, so it only appears with a cylinder.
- Add (ADD). The extra power for reading and close work in multifocal contact lenses. It may say High, Medium or Low, or give a number such as +2.00.
- Dominance (D or N). Some multifocal contact lenses have a D or an N after the add. It marks the dominant (D) and the non-dominant (N) eye.
The measurements of your prescription
- Base curve (BC). How curved the lens is, for example 8.4 or 8.6. Your optometrist matches the curve of the lens to the curve of your eye for a good fit.
- Diameter (DIA). The length of the lens from edge to edge, for example 14.3. It makes sure the lens covers the right parts of your eye.
The box
Most contact lens prescriptions also have a brand name, so that you can reorder your lenses, and the box shows the expiry date.
Contact lenses are sold only on a current prescription. If yours is out of date, or you would like to start wearing contact lenses, book an eye test.