No worries—we’ve got you covered. Here are some terms you’ll see on your prescriptions:
OD: This abbreviation stands for “oculus dexter,” which is “right eye” in Latin.
OS: This abbreviation stands for “oculus sinister,” which is “left eye” in Latin.
Sphere (SPH): Sphere indicates how strong your lenses need to be. This will be accompanied by a plus (+) or minus (-), which indicates whether you’re farsighted or nearsighted.
Cylinder (CYL): Cylinder is the correction for astigmatism. Astigmatism means that the shape of your cornea prevents you from seeing with perfect sharpness. If you have a cylinder included on your contact lens prescription, that usually means you wear toric lenses.
ADD: This is used when you require a prescription for both distance and reading in your glasses or contact lenses. It can be shown as an ADD value with a plus (+) sign with a number or, for certain contact lens brands, a description like ""high"" or ""low."" An ADD indicates that you may need progressive or multifocal lenses. It also may give you the ability to order one of three types of single-vision correction: distance, reading, or intermediate correction.
Base curve (BC): For contact lenses, the base curve helps the lens fit properly. This usually is a number between 8 and 10 that measures the curve of a contact lens.
Diameter (Dia): This is the width across a contact lens in millimeters. Most contact lenses are 13–15 mm wide.
Contact lens prescriptions and eyeglass prescriptions are not the same. They are significantly different because eyeglass lenses are positioned approximately 12 millimeters from your eyes, whereas contact lenses rest directly on the surface of your eyes. The power of a contact lens will be slightly less nearsighted or slightly more farsighted.
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