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How do I read my contact prescription, and contact box?

Although the data that makes up your contact lens prescription may seem intimidating, a contact lens prescription is intended to keep your eyes safe and comfortable, in addition to making sure you’ll receive optimum vision correction. If you’re in the United States, your contact lens prescription is yours to keep. In fact, your optometrist is required to give you a copy of your prescription at the end of your contact lens exam and fitting – even if you didn't ask for it.

Here are the definitions of abbreviations used in a typical contact lens prescription. These abbreviations are also found on the end/side of your existing contact lens box:

Abbreviation Meaning Definition
OD Oculus Dexter Latin for "Right Eye"
OS Oculus Sinister Latin for "Left Eye"
OU Oculus Uterque Latin for "Both Eyes"
SPH Sphere The overall power of the lens.
BC Base Curve Back curve of a contact lens measured in millimeters.
DIA Diameter Diameter of your lens from one edge to the opposite edge.
CYL Cylinder A "+" refers to farsightedness, a "-"refers to nearsightedness.
AX Axis A measurement design to correct astigmatism.
ADD Add Power Typically found in prescriptions for reading or close-up vision.

In addition to the above information, your contact lens prescription will include information about the brand and, in the case of colored or cosmetic lenses, a reference to the color or design. The information may seem complicated, but once you’re accustomed to the abbreviations it's very straightforward.

Although many assume a contact lens prescription is the same as an eyeglass prescription, the two are not interchangeable. In addition to lens power, a contact lens prescription contains several other pieces of information related to the size, color, brand, and expiration dates of the lenses.

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