If you have just received a new prescription for contact lenses, you may be wondering what all the numbers and letters mean. The good news is that it’s all understandable once you realize that a prescription for contact lenses is very different than one for eyeglasses. Prescriptions for contact lenses need additional information because of how the lenses are placed on your eyes.

Reading Your Contact Lens Prescription

OS refers to the left eye and OD refers to the right eye. You will see a set of numbers under each of these abbreviations. Each one of your eyes may need a different prescription to correct your specific vision problem.

PWR or SPH is the amount of correction your eyes need to bring your vision to 20/20. This is measured in an optical unit called a diopter. This number will either have a minus sign in front of it, (if you are nearsighted) or a plus sign (if you are farsighted). You can determine if your prescription is strong based on how far away from zero this number is. It’s common to have a different prescription for each eye.

BC stands for the back curvature of the contact lens. This is measured in millimeters and is generally between 8 and 10. The exactness of this number is important because it represents how the contacts will match up with the cornea. This is the part of the eye that refracts, or bends the light rays, in order to create an image for you to see. Sometimes, there may be no BC because the brand of lenses that is prescribed for you is only available with one base curve.

DIA is the abbreviation for diameter which is the total distance across the surface of the contact lens. This number is generally between 13 and 15 millimeters. This part of the prescription shows where on your eye the contact lens will sit. If the measurement is off, the lens will feel uncomfortable and may even scratch your eye.

CYL stands for cylinder value which is the amount of power needed to correct your specific astigmatism. It is measured in diopters between -4 and +4. For hyperopic astigmatism, or farsightedness, the number is positive; for myopic astigmatism, or nearsightedness, the number is negative.

AXIS is measured in degrees and refers to the amount of rotation the cylinder must rotate to compensate for the oval shape of an astigmatic lens.

ADD refers to a prescription added for close work, like reading, or for bifocal lenses.

Color is just what it says; the contact lenses can be matched to your eye color or you can have a different color to cosmetically change your natural one.

Brand Name may be what your eye care provider feels would be best for you. Your prescription may also include how often to replace the contact lenses and suggest a replacement schedule.

The eye care industry uses a standard code and measurement to create your prescription.  Consider your contact lenses to be a medical device which means that all of these letters, numbers, and abbreviations are on the prescription to enable you to see better. Although your prescription might look like alphabet soup, it holds the perfect recipe for contact lenses that are designed specifically for you.

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