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Understanding your contact lens prescription

You’ve visited the eye doctor and obtained a prescription for eyeglasses or contacts, but when you look at your prescription, all you see is letters and numbers. For the uninitiated, an eye prescription can be confusing. It’s actually not too complicated, once you know what those letters and numbers mean.

RUMI Optical practitioners use standard terms, abbreviations, and measurements to read and write contact lens prescriptions. You have probably wondered what the incomprehensible scribbles of your ophthalmologist mean and if you could ever learn to decipher them. And although you don’t need to know all of the abbreviations and numbers in your optical prescription, it is useful to understand some of them, especially if you are going to shop online.

A contact lens prescription is typically made up of the following:

Base curve (BC)

This number indicates how curved your contact lens is. Your optician will try and match the curve of your contact lens to the curve of your eye to find the best fitted contact lens for you. E.g. BC 8.4.

Diameter (DIA)

This stands for Diameter and is the length of the contact lens from one edge of the lens to the other. This is effectively the size of the contact lens and is used to make sure the contact lens covers the correct parts of your eye. E.g. DIA 13.8.

power (PWR) or sphere (SPH)

Power (pwr) or Sphere (sph) or Dioptre (D) is the power of the lens needed to correct your long or short-sightedness and is measured in Dioptres (D). A minus (-) sign indicates that you are short-sighted, whereas a plus (+) sign shows that you are long-sighted. The higher the number, the stronger your prescription.

cylinder (CYL)

This is the amount of astigmatism you have and is to do with how curved the structures in your eye are. If this section is empty you do not have astigmatism and are just long or short sighted. If you do have astigmatism, a value will be entered in this box along with an Axis. E.g. Left eye: -2.25, Right eye: -2.25.

axis (AXIS)

The axis is the measurement calculated in degrees that is required to bend light to correct the irregular shape of the cornea. This is essentially the orientation needed for your CYL to work properly. This number will be a higher number, such as 090 or 160, depending on how slanted your CYL needs to be

power (ADD)

Sometimes, it may be necessary for you to have contact lenses with bifocals in them. If this is the case, your prescription may have a column or row for ADD, which is the amount that the lens needs to be adjusted for the bifocal lenses. This term is measured in diopters

color (COLOR)

There may be a reason your prescription includes the term color. This is a field that indicates if you requested a certain kind of contact lens to enhance to color of your eyes. This can also indicate a special kind of contact, such as "cat eye" or some other eye changing quality. The special features available will differ depending on the brand you need. Ask your optometrist about your options based on your current condition

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