How to Read a Contact Lens Prescription
- 1). Understand the points that are commonly listed in a prescription. This includes the power, the base curve, the diameter and the brand of a lens. For special prescriptions, such as bifocal or astigmatism, there is usually additional information as well.
- 2). Learn the common abbreviations used by the doctor. The abbreviation for the left eye is OS and the abbreviation for the right eye is OD. "Base curve" is indicated with BC, "power" with PWR" and diameter" with DIA. Additional abbreviations include CYL for "cylinder" and AXIS (used for astigmatism), as well as ADD for "add power," which is used for bifocal prescriptions. There is a corresponding number with each of these measurements for both the right eye and the left eye.
- 3). Grasp the meaning of each of these measurements. The measurement of diameter (given in millimeters) is the distance from one edge of the contact to the other. This is important because it determines how the contact will rest on your eye, which is crucial for the overall comfort of the lens.
- 4). Realize that the power of a lens is the strength (measured in diopters) required to bring a given patient to perfect 20/20 vision. A minus sign indicates nearsighted (myopia) and a plus sign indicates farsighted (hyperopia). The further from 0 the power is, the stronger the prescription.
- 5). Understand that the base curve measurement is used to show the back curvature of a contact lens, and is given in millimeters. For greatest comfort, the base curve should match the curve of the cornea. The lower the base curve value, the steeper the cornea of a patient's eye. Some brands of contacts only come in one standard base curve value, so this measurement might not be included on some prescriptions.
- 6). Find an additional piece of information on a prescription: the brand. It is unlawful for a contact lens retailer to sell a patient a different brand of contact lens than the one indicated on the prescription.
