Throughout each day, we consistently go through the motions of protecting our vital organs; we choose to wear a helmet when biking, and exercise to improve our cardio health without so much as a second thought. When it comes to our own two eyes, it is just as important to be defensive; especially as wearing contact lenses without a prescription from a qualified eye doctor can be risky.
Contact Lenses vs. Eyeglass Lenses
Though you may not have thought of them as such, contact lenses are a medical device. Therefore, it is illegal to purchase them without a valid eye prescription written by an eye care physician. This law extends to non-prescription cosmetic lenses as well, including colored lens or special effect contacts. There are practical reasons for having prescriptions and products covered under state and federal laws. For example, some patients believe their eyeglass prescription is also valid for their contact lens prescription. This is not the case.
Contact lenses fit over the cornea of your eye. Consequently, your contact lens prescription will have a different lens power than the lens in your eyeglasses, in addition to other measurements related to the size of the lens. Special measurements are needed to not only insure better vision for the patient, but to avoid causing eye irritation, tissue damage, swelling from infection, and other vision risks caused by ill-fitting lenses.
Understanding Your Contact Lens Prescription
In order to understand how contact lens prescriptions work, it is helpful to understand how to read your prescription. Your script contains specific measurements based on your own unique eyes, each of which is equally important. Not realizing this, many people purchase ill-fitting contacts because they overlook the brand of contact their physician has written their prescription for. To illustrate how this happens, we’ll create a quick analogy.
Let’s say your doctor writes a prescription for branded contact lenses specified with a BC value. You see a coupon for a different brand and think, “These contacts are all the same, why not save money?” You purchase the brand not prescribed by your eye doctor and save a few dollars.
In your original prescription, however, your doctor specified a BC value. A normal BC value refers to the curve of your eye, and runs 8.0 to 10.0. BC values are similar to women’s shoe sizes: Just because you wear a size 7 in a Bandalino slingback, does not mean you wear a size 7 in a running shoe. In speaking of a contact lens and its BC value, a prescription for an 8.6 in one brand may fit like a BC value of 8.7 in another. That means, when the patient elected to purchase a different brand of contact lenses than their physician prescribed, they wound up paying for contact lenses that do not fit the back curvature of their eye.
Understanding your contact lens prescription and ordering your contacts based on the specific instructions your eye doctor intended will help you keep your eyes safe and healthy. The guide in the table below is designed to help you understand what all the abbreviations and numbers mean on your own contact lens prescription.
How to Read A Contact Lens Prescription
- PWR - Refers to the Diopters needed to sharpen vision to 20/20. A Plus sign with a numeral will mean it is a prescription for farsightedness. A minus sign with a numeral will be a prescription for nearsightedness.
- BC - BC stands for back curvature measured in millimeters of your eye. Measurements range from 8 to 10. Prescriptions that do not have a BC value come in one base curve, and no other sizes.
- DIA – Refers to the diameter of the lens needed. This measurement determines where the edge of the contact lens will set in the eye and it is extremely important to ensure a comfortable fit.
- CYL - Cylinder numbers can range between -4.00 and +4.00. This measurement is for patients who need lenses that are for astigmatism. Lens prescriptions for these lenses will contain two additional numbers that are related to the astigmatism.
- AXIS – The Axis is a number for an astigmatism prescription between 0 and 180, which will be expressed in degrees.
- ADD - When patients require bifocal or multifocal corrective contact lenses, they will have a number that is listed under add. It means to add power or add strength.
- COLOR – Color and style prescription names differ from one brand of contact lenses to another. This value refers to the color or shade of the contact lens.
- Brand - By law in the United States, all contact lens prescriptions must list a brand. The law states that the contact lens retailer must sell you the specified brand and not substitute it for any other brand.
Just because you’re buying online doesn’t mean you won’t need a doctor’s prescription; Replace My Contacts is proud to uphold medical ethics by requiring every purchaser to include one with their order to get lens like Acuvue, Air Optix and more.