What Does Rx Mean for Contact Lenses?

A contact lens Rx, or prescription, includes several measurements that result in a well-fitting lenses.

Contact lenses are medical devices that can only be purchased with a prescription. Visit a licensed optometrist or ophthalmologist to obtain a prescription or Rx. Understanding how to read your Rx will help you identify your eye-care needs.

OD, OS or OU

OD refers to the Latin phrase "oculus dexter," which means right eye; measurements listed under the OD column applies to the right eye only. OS refers to the Latin phrase "oculus sinister," which means left eye; measurements listed under OS apply to the left eye only. If both eyes include the same measurements, your prescription will be labeled "OU," which refers to "oculus uterque," meaning each eye.

PWR

Referring to lens power, this measurement describes how much correction each eye needs. Measured in dioptres, a negative sign indicates myopia, or nearsightedness, while a positive sign indicates hyperopia, or far-sightedness.

BC

Referring to base curve, BC indicates the curve of the lens, measured in millimeters.

DIA

Measuring diameter, DIA indicates the width from one edge to the opposite edge of the lens.

Toric Lenses

Lenses that correct astigmatism, known as toric lenses, will also include the additional measurements Cyl and Axis. Cyl refers to the strength of the astigmatism while Axis refers to its orientation.

References

• All About Vision: Understanding Your Contact Len Prescription
• Bausch and Lomb: Contact Lenses