Eyeglasses and Contact Lenses
Lenses to correct or improve vision
There are two types of lenses prescribed to correct or improve vision. These include:
Eyeglasses. These are the most common form of eyewear used to correct or improve many types of
vision problems. Eyeglasses are a frame that holds two pieces of glass or plastic
that correct refractive errors. Refractive errors can include difficulty seeing far
away (nearsightedness or myopia), difficulty seeing close up (farsightedness or hyperopia),
and blurring due to an unevenly shaped cornea (astigmatism). Eyeglasses work by adding
or subtracting focusing power to the cornea and lens.
Contact lenses. Contact lenses are worn directly on the cornea. Like eyeglasses, contact lenses help
correct refractive errors. They do this by adding or subtracting focusing power to
the cornea and lens.
How to read an eyeglass prescription
The lens power of eyeglasses is measured in diopters. This measurement shows the amount
of power needed to focus images directly onto the retina. When looking at an eyeglass
prescription, you will see the following abbreviations:
O.D. Oculus dextrus means the right eye (sometimes the abbreviation RE is used).
O.S. Oculus sinister means the left eye (sometimes the abbreviation LE is used).
The eyeglass prescription may also have the following measurements:
This number shows the extent of the nearsightedness or farsightedness.
This number means the amount of astigmatism. Astigmatism is an unevenly shaped cornea
that causes blurring.
This number describes the astigmatism in degrees from the horizontal axis. Most left
and right eyes have a similar axis of astigmatism.
Bifocal prescriptions often have an additional measurement listed on the prescription
as "add." This shows the strength of the lens for near vision. Bifocals are used to
correct both nearsightedness and farsightedness.
What are the different types of eyeglass lenses?
The type of lenses used in eyeglasses depends on the type of vision problem. They
Concave lenses. These are thinnest in the center. They are used to correct nearsightedness. The numerical
prescription in diopters is always marked with a minus (-) symbol.
Convex lenses. These are thickest in the center. They are used to correct farsightedness. The numerical
prescription in diopters is always marked with a plus (+) symbol.
Cylindrical lenses. These curve more in one direction than in the other. They are used to correct astigmatism.
Facts about contact lenses
More than 30 million Americans wear contact lenses. Of those, 80% use daily wear soft
lenses. Currently, there are four types of contact lenses:
The soft, water-absorbing lens
The rigid, gas-permeable lens
Other rigid lenses
Other flexible, non-water-absorbing lenses
Reading a contact lens prescription
The prescription for contact lenses includes more information than what is available
in the prescription for eyeglasses. Special measurements will need to be taken of
the curvature of the eye. In addition, the eye care provider will determine if the
eyes are too dry for contact lenses. They check if there are any corneal problems
that may prevent a person from wearing contact lenses. Trial lenses are often worn
for a period of time to make sure they fit correctly.
The contact lens prescription often includes this information:
Eye care providers are required by federal law to give you a copy of your contact