Contact lens prescriptions must be obtained from an eye care practitioner, either an optometrist or an ophthalmologist. Even if a patient already has a prescription for glasses, additional tests and measurements are required for proper lens fitting.
Refractive Power
The refractive power is the amount of correction the lens must provide in order to correct vision. A minus sign is given for prescriptions to correct nearsightedness, and a plus sign is given for prescriptions to correct farsightedness.
Base Curve
The base curve, BC, measures the curvature of the cornea in millimeters. This measurement ensures a proper lens fitting.
Diameter
The diameter, DIA, measures the actual diameter of the contact lens. This measurement determines where the edges of the lenses will rest on the eye.
Cylinder and Axis
The cylinder, measured in diopters, measures the amount of astigmatism present. The axis is the measurement required for the contact lens to correct the astigmatism.
Add Power
Add power is utilized in bifocal contact lenses. The add power helps the patient visualize items that are close.
Brand and Color
United States law requires contact lens prescriptions to indicate at least one brand name of contact lens, according to EyeDoctorGuide.com. Contact lens sellers may only provide patients with the brand listed on the prescription. Contact lenses can also be used to change the color of the eyes, and the prescription would indicate the color chosen.
