Contact lens and eyeglass prescriptions are two different things. Eyeglasses are worn about 12 millimeters away from your eyes while contact lenses are directly on the surface of your eyes which is why both descriptions cannot be the same.
For you to choose the right contact lenses and eyeglasses, you must have two separate prescriptions and not just mere conversions.
The Difference Between Contact Lens and Glasses Prescription
Similar to an eyeglass prescription, contact lens prescription measures the lens power needed to compensate for the refractive error – may it be nearsightedness, farsightedness, or astigmatism.
Depending on the degree of your refractive error, your contact lens prescription may differ significantly from your glasses prescription with all the additional specifications required including the type of contact lens and its fitting. These specifications include:
- Base curve. This pertains to the back surface curvature of the contact lens. The proper base curve is measured by the shape of your cornea to produce a proper fit that is not too loose nor too tight.
- Diameter. This specifies the overall size of the lens. This typically ranges from 13.5 to 14.5 mm for soft contact lenses and 8.5 to 9.5 mm for rigid gas permeable (GP) contacts.
- Lens brand or material. Each lens material contains a specific level of oxygen permeability (“breathability”). This is extremely important to be specified in your prescription especially if you intend for extended wear contact lenses.
- Expiration date. A contact lens Rx is usually valid for one year and is normally required before purchasing new contact lenses. Eyeglass prescriptions on the other hand mostly expire after two years.
You are entitled to have a copy of both of your glasses and contact lens prescriptions. However, a contact lens prescription cannot be given without a contact lens fitting. It is illegal for your eye doctor to withhold your prescriptions from you.
Is Anyone Qualified to Get a Contact Lens Prescription?
Not everyone who wears eyeglasses can opt to wear contact lenses successfully. Eye conditions such as dry eyes, blepharitis, and sensitive corneas can make wearing contact lenses unsafe and uncomfortable.
A contact lens prescription must be written by a licensed eye care professional before you can purchase even just colored contact lenses or special-effect contact lenses that are only intended for cosmetic purposes. Regardless of its purpose, may it be medical or cosmetic, contact lenses are still medical devices. Selling any type of contact lenses without a prescription is considered illegal.