How Is The Prescription For Eyeglasses And Contacts Different?
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The prescription for your eyeglasses and contacts are different. The lenses in your eyeglasses are designed to be worn about 12 millimeters from the surface of your eyes while your contacts are worn directly on the surface—this difference in distance from your eyes makes your prescription quite different.
Therefore, you will need a prescription for eyeglasses and a separate prescription for contact lenses if you wish to wear both.
How is the prescription for eyeglasses and contacts different?
A contact lens prescription includes the lens power necessary to correct your refractive error— astigmatism, nearsightedness (myopia), and/or farsightedness (hyperopia) — just like your glasses prescription.
In order to make sure your vision is functioning at its best, the power prescribed on for your contacts may be quite different than the one on your glasses prescription, depending on the type of contacts you need and the degree of your refractive error.
Glasses prescriptions do not include as many specifications as contact lens prescriptions. These differences are determined during a comprehensive exam and fitting for your contacts. These additional specifications may include:
A base curve measurement (BC) is the curvature of the back surface of the lens. The shape of your cornea determines the base curve. The base curve ensures that your lenses fit just comfortably.
The lens diameter (DIA) identifies the size of the lens. The lens diameter and base curve determine the fit of the lens. The typical soft contact lens diameter is 13.5 to 14.5 millimeters, and rigid gas permeable lenses range from 8.5 to 9.5 millimeters.
A contact lens prescription will also include the lens brand or material. It is important to list the material because the “breathability” (degree of oxygen permeability) differs. If you find that you occasionally fall asleep with your contacts in or wear extend wear contacts, this is important.
As a rule, the expiration date of your prescription is about one year. When your prescription expires, you will need to follow up with your doctor before getting new contacts so he can make sure you don’t need a new prescription. Most eyeglass prescriptions expire after 2 years and are regulated under state law. Your doctor is required by law to give you access to your prescriptions for both eyeglasses and contacts. After you have had an eye exam, you are entitled to a copy of your prescription. You will, however, have to have a contact lens fitting before you can get a prescription for contact lenses.
Are contact lenses available to everyone?
Contact lenses are not an option for everyone who wears glasses. There are a number of conditions and circumstances in which your doctor may decide that contact lenses are not an option for you. For instance, it may be uncomfortable or unsafe to wear contacts if you have dry eyes or blepharitis. You may have sensitive corneas and are just unable to adapt to wearing contacts.
What about colored contact lenses?
Even if you just want to change the appearance of your eyes with a non-prescription special effect or colored contacts, you are still required by law to have a prescription. Regardless of whether you use it for looks or vision correction, a contact lens is a medical device and must have a legitimate prescription from an eye doctor. It is illegal to sell contact lenses without a prescription.