Millions of Americans wear prescription glasses and contacts in order to correct vision problems. While many people can wear both glasses and contacts according to their preference, there are those that are not able to wear contacts due to conditions such as dry eyes or blepharitis, which can make wearing contacts uncomfortable or unsafe.
Because it is so common for people to wear both glasses and contacts, many assume that their prescriptions for both items are the same. However, this is untrue. In most cases, these prescriptions will differ.
Why Are They Different?
Eyeglasses are usually worn about 12 millimeters from the eye, while contacts are worn directly on the eye. Because of this difference, the prescriptive power will not be the same to make up for the difference in distance from the eye.
In addition, in the case of contact lenses, the eye doctor will need to measure the curvature of the cornea in order to prescribe the correct curvature and size of lens to the patient.
Differences in Exams
In order to receive a prescription for both eyeglasses and contact lenses, a patient will need to have different exams done. A proper eyeglass prescription can be determined during a comprehensive eye exam, which generally includes tests to check vision sharpness, look for signs of glaucoma, and check the fluid pressure in the eye. The patient’s eyes may also be dilated, giving the eye doctor an opportunity to see if any eye conditions exist, or any signs of serious health conditions or eye conditions are present. After the doctor completes all of the necessary tests, a prescription will be written out according to whatever strength is needed to correct any vision problems.
If the patient desires to wear contact lenses, an additional exam will need to take place. This exam will include special tests that will allow the doctor to evaluate the patient’s vision with contacts. Tests will be done to determine the correct size and type of contacts required, and the doctor may also do a tear film evaluation to determine if the eye produces enough tears for the patient to be able to comfortably wear contacts.
Additional specifications will be included on a contact lens prescription that are not included on a prescription for glasses. These specifications include the following:
- Base curve, which is determined by the shape of the cornea and ensures a fit that is not too loose or too tight
- Diameter, which specifies the overall size of the lens
- Lens brand or material, which is important if the wearer wants extended wear contacts
- Expiration date, which is generally one year from the date the prescription was written
Attempting to use one prescription in place of the other may damage the health of the eyes. It is very important that prescription glasses and contacts are used only as directed by the eye doctor to ensure the health and safety of the wearer.