Eye Exams for Contact Lenses
By Michelle Stephenson;
additional contributions by Marilyn Haddrill;
reviewed by Dr. Valerie Kattouf
If you already wear or are interested in contact lenses, make sure you say so when you schedule your appointment for an eye exam.
You'll need some extra time and additional tests such as an evaluation of your eye's surface
(cornea) so that your eye doctor can make sure you
receive a proper contact lens fitting.
You'll first undergo a routine eye exam in which your eye doctor will use a bright light to view and assess the
structure of the outside of your eye. Your eye doctor also will observe how well your eye muscles function. A
standard visual acuity test will be given to determine your ability to see letters or numbers on an eye chart.
If you do require vision correction, then the eye doctor will determine the corrective lens prescription that
will give you the best vision. [See also: What To Expect From a Comprehensive Eye Exam.]
What To Expect During a Contact Lens Fitting
Now that the standard eye exam has been completed, your eye doctor will need additional information
before you can be fitted for contact lenses. You may be asked general questions about your lifestyle and
preferences regarding contact lenses, such as whether you might want to change your eye color with
color contact lenses or if you're
interested in options such as
daily disposables
or
overnight wear.
Your eye doctor may also discuss the option of
rigid gas permeable (RGP or GP) contact lenses,
although most people today are fitted with soft lenses.
Your eye doctor may question you about how you might want to correct vision problems related to aging.
At about age 40 or maybe older, you will develop a condition known as
presbyopia that decreases your ability
to see clearly at all distances. To correct presbyopia, your eye doctor may offer you the choice of
multifocal
or bifocal contact lenses or
monovision,
in which one contact lens corrects for near vision and the other
contact lens corrects for distance vision.
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An eye doctor uses lenses with magnification to inspect the surface of an eye.
This type of evaluation is needed before you are fitted with contact lenses. (Photo courtesy of National
Eye Institute, National Institutes of Health) | |
Other Contact Lens Measurements
Just like one shoe size doesn't fit all, one contact lens size doesn't fit all.
If the curvature of a contact lens is too flat or too steep for your eye's shape,
you could experience discomfort or even eye damage. Other aspects of a contact lens fitting include:
- Measurement of your eye's surface and curvature: An instrument called a keratometer,
which is a type of digital camera, will be used to measure the curvature of your eye's clear
front surface (cornea). With one version of the instrument, you sit and face the instrument.
You then place your chin on a brace so that your head is held still while the instrument
photographs your eye. The keratometer automatically assesses images of your cornea and
creates mathematical representations of the curvature of your eye's surface (K-readings).
These measurements help your eye doctor determine the proper curve and size for your contact lenses.
Because the keratometer measures only a small, limited section of the cornea, additional computerized
measurements of your cornea (corneal topography) may be done. Corneal topography provides extremely
precise details about surface characteristics of the cornea by analyzing photographic images taken
of the way light projected into your eye travels. With one version of a corneal topographer, you are
seated with your forehead resting against a curved brace. Circular patterns of light then are beamed
into your eye for photographic analysis. A computer creates and prints out the resulting surface "map"
of your eye, with different contours represented by varying colors.
[See also: Refraction: How the Eye Sees.]
If your eye's surface is found to be somewhat irregular because of
astigmatism, you may require a
special design of lens known as a toric contact lens that is shaped to offset distortions of your
eye to provide sharper vision. At one time, only rigid contact lenses could correct for astigmatism.
But there are now many brands of soft toric lenses. Toric lenses also are available in disposable,
multifocal, extended wear, and colored versions.
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