Eye Glasses and Contact Lenses
Lenses for correcting or improving vision:
There are two types of lenses prescribed for correcting or improving vision. These
include:
- eyeglasses (also called spectacles)
Eyeglasses, the most common form of eyewear used to correct or improve many types of
vision problems, 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.
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.
How to read an eyeglass prescription:
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:
| O.D. – Oculus dextrus simply refers to
the right eye (sometimes the abbreviation RE is used). |
O.S. – Oculus sinister
refers to the left eye (sometimes the abbreviation LE is used). |
In addition, the eyeglass prescription may also contain the following
measurements.
| Sphere |
This number measurement reflects the extent of the
nearsightedness or farsightedness. |
| Cylinder |
This number measurement refers to the amount of
astigmatism (an irregularly shaped cornea which causes blurring) in the eye. |
| Axis |
This number measurement describes the astigmatism in
degrees from the horizontal (most left and right eyes have the same axis in astigmatism)
axis. |
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.
| Did You Know? 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 that you can shop for the best
value in eyewear. |
What are the different types of eyeglass lenses?
The type of lenses used in eyeglasses depends on the type of vision problem, and may
include:
- Concave lenses are thinnest in the center. Used to correct
nearsightedness (myopia), the numerical prescription in diopters is always marked with a
minus (-) symbol.
- Convex lenses are thickest in the center, like a magnifying glass. Used
to correct farsightedness (hyperopia), the numerical prescription in diopters is always
marked with a plus (+) symbol.
- Cylindrical lenses curve more in one direction than in the other and
are often used to correct astigmatism.
Facts about contact lenses:
Almost 25 million Americans wear contact lenses, half of whom wear daily wear soft lenses.
Currently, there are five types of contact lenses in use:
- the original "hard" lens
- 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 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:
- contact lens power (measured in diopters, like eyeglasses)
- contact lens base curve
- diameter of the lens
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.
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