Eyeglasses and contact lenses are the two types of lenses prescribed for correcting or improving vision. We have an in-house optical center that provides prescription eyewear. Learn more about Optical for Children.
Eyeglasses are a frame that holds two pieces of glass or plastic, which have been ground into lenses to correct refractive errors. Refractive errors can include nearsightedness or myopia (difficulty seeing far away), farsightedness or hyperopia (difficulty seeing close up), and astigmatism (blurring due to an irregularly shaped cornea). Eyeglasses perform this function by adding or subtracting focusing power to the eye's cornea and lens.
The lens power of eyeglasses is measured in diopters. This measurement reflects the amount of power necessary to focus images directly on to the retina. When looking at an eyeglasses prescription, you will see the following abbreviations:
In addition, the eyeglass prescription may contain the following measurements:
Bifocal prescriptions, which correct both nearsightedness and farsightedness, usually have an additional measurement listed on the prescription as "add," to indicate the strength of the lens. By federal law, an eye doctor is required to provide an eyeglass prescription following an eye exam at no extra cost. In addition, under federal law, you have the right to a copy of your eyeglass prescription, so you can shop for the best value in eyewear.
The type of lenses used in eyeglasses depends on the type of vision problem and may include:
Contact lenses are worn directly on the cornea of the eye. Like eyeglasses, contact lenses help to correct refractive errors and perform this function by adding or subtracting focusing power to the eye's cornea and lens.
Almost 36 million Americans wear contact lenses, and a majority wears daily wear soft lenses. Currently, there are four types of contact lenses in use:
The prescription for contact lenses includes more information than what is available on the prescription for eyeglasses. Special measurements will need to be taken of the curvature of the eye. In addition, the physician will determine if the eyes are too dry for contact lenses and if there are any corneal problems that may prevent a person from wearing contact lenses. Trial lenses are usually tested on the eyes for a period of time to ensure proper fit.
The contact lens prescription usually includes the following information:
Unlike eyeglass prescriptions, eye care specialists are not required by federal law to give you a copy of your contact lens specifications. Although, many eye care specialists will give you a copy if you request one.
