How To Read Contact Lens Prescription

Do you want to learn how to read contact lens prescription? Ever wondered why your doctor charges you extra to have your eyes examined for contact lenses versus glasses, and why it is you can’t simply use your prescription for glasses to get a pair of contacts? Or, do you just want to know what all the numbers written on that piece of paper mean? Both contact lenses and glasses help you see and have similar prescriptions, but there’s some additional information you need before you go sticking things into your ocular sockets. Here, we’ll discuss how to read a contact lens prescription, so that as a contact connoisseur, you’ll be in the know.

A basic contact lens prescription can consist of many things: these are labeled Eye, Power (Sphere), BC, DIA, CYL, AXIS, ADD, COLOR, and Brand.

  1. Eye is pretty self-explanatory. It tells the person preparing your contact lenses which of your two eyes has what prescription. The differentiations are OS (oculus sinister, Latin for left eye) and OD (oculus dexter, for right eye). If there’s something listed OU, it doesn’t mean Oklahoma University; it’s optometrist shorthand for oculus uterque–Latin for both eyes, and it means that that prescription can be applied to both eyes.
  2. Next is power. This tells the prescription filler what strength lens per the amount of correction your eye needs. Negative numbers mean that that particular eye is nearsighted; positive numbers stand for correction of farsightedness. This number will range from -20.00 to +20.00.
  3. BC is the first of the things that makes your contact prescription different from the one for your glasses; it stands for base curve, a measurement to fit the lens so that it either matches or compliments the curve of your cornea. This number rangers from 8.0 to 10.0 millimeters. The lower this number is, the steeper your cornea is curved.
  4. DIA is yet another contact lens-specific prescription term. It measures in millimeters the distance from one end to the other (the diameter) of your contact lens. This number is critical, as it is the number that determines where on your eye the edges of the contact lens will rest. If it’s too small or two large, the lens will not fit properly, and it could result in anything from the loss of your contact lens to irritation or abrasion of the eye.
  5. CYL is short for cylinder. If you have astigmatism (an eye disorder where the eye is curved unevenly), this number is measured in diopters, and measures how much astigmatism you have. It is used in lenses that correct for astigmatism. Negative numbers correct myopic astigmatism; positive corrects for hyperopic astigmatism. 
  6. AXIS is another astigmatism-related number, measured in degrees, and shows the orientation of the cylinder in the lens.
  7. ADD stands for the measurement given to bifocal contact lenses, to correct for far-sightedness in close-up tasks, much like the specific region on a pair of glasses would. It is measured in diopters and is always understood to be positive.
  8. COLOR is just that. If you asked for contact lenses to change or enhance your eye color (or change your eye altogether, as is the case with special effects lenses), it’s written here.
  9. Finally, BRAND stands for brand name. In the United States, your prescription must contain a particular brand of contacts, and by law, you can only be sold that particular brand of contacts. There are some cases of “private-label” contacts, sold only by certain eye care pros; in these cases, you might be allowed to substitute an equivalent national or other private-label lens.

Now that you know how to read your contact lens, you also need to know that it has a date written on it; that date is what determines when your prescription expires. Your prescription, by law, is valid for at least a year, but it is usually valid for up to two years. Know, too, that just having a glasses prescription won't suffice for getting a pair of contacts, but a contact lens prescription can get you glasses. So, if you can’t decide right now between contacts and glasses, shell out the extra bucks for the contact prescription.

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