A comprehensive
eye exam includes a number
of tests and procedures to examine and evaluate the health of your eyes and the
quality of your vision. These tests range from simple ones, like having you
read an eye chart, to complex tests, such as using a high-powered lens to
examine the health of the tissues inside of your eyes.
Here are some tests you are likely to
encounter during a routine comprehensive eye exam:
Retinoscopy
This
test helps your doctor get a good approximation of your eyeglasses
prescription. For retinoscopy, the room lights are dimmed and an instrument
containing wheels of lenses (called a phoropter) is positioned in front of your
eyes. You will be asked to look at an object across the room (usually the big
“E” on the wall chart or screen) while your doctor shines a light from a
hand-held instrument into your eyes from arm’s length and flips different lenses
in front of your eyes.
Based
on the way the light reflects from your eye during this procedure, your doctor
can get a very good idea of what your eyeglasses prescription should be. This
test is especially useful for children and non-verbal patients who are unable
to accurately answer the doctor’s questions.
With
the widespread use of automated instruments to help determine eyeglass prescriptions
today, many doctors forgo performing retinoscopy during comprehensive eye exams.
However, this test can provide valuable information about the clarity of the
internal lens and other media inside the eye. So doctors who no longer perform
this test routinely may still use it when examining someone who may be at risk
of cataracts or other internal eye problems.
Refraction
This is the test your doctor uses to
determine your exact eyeglasses prescription. During a refraction, the doctor
puts the phoropter in front of your eyes and shows you a series of lens
choices. He or she will then ask you which of the two lenses in each choice (“1
or 2,” “A or B,” for example) make the letters on the wall chart look clearer.
Based on your answers, your doctor will
determine the amount of nearsightedness, farsightedness and/or astigmatism you
have, and the eyeglass lenses required to correct these vision problems (which
are called refractive errors).
Autorefractors
and aberrometers
Your eye doctor also may use an
autorefractor or aberrometer to help determine your glasses prescription. With
both devices, a chin rest stabilizes your head while you typically look at a
pinpoint of light or other image.
An autorefractor evaluates the way an
image is focused on the retina, where vision processing takes place, without
the need for you to say anything. This makes autorefractors especially useful
when examining young children or people who may have difficulty with a regular (“subjective”)
refraction. Automated refractions and subjective refractions are often used
together during a comprehensive exam to determine your eyeglasses prescription.
An aberrometer uses advanced wavefront
technology to detect even obscure vision errors based on the way light travels
through your eye.
Cover
test
While there are many ways for your eye
doctor to check how your eyes work together, the cover test is the simplest and
most common.
During a cover test, the eye doctor will
have you focus on a small object at distance and will then cover each of your
eyes alternately while you stare at the target. As they do this, eye doctors
observe how much each eye has to move when uncovered to pick up the fixation
target. The test is then repeated as
you focus on a near object.
Cover tests can detect even very subtle
misalignments that can interfere with your eyes working together properly (binocular
vision) and cause amblyopia or “lazy eye.”
Slit-lamp
examination
The slit lamp is an instrument that the
eye doctor uses to examine the health of your eyes. Also called a
biomicroscope, the slit lamp gives your doctor a highly magnified view of the
structures of the eye, including the lens behind the pupil, in order to
thoroughly evaluate them for signs of infection or disease.
The slit lamp is basically an illuminated
binocular microscope that’s mounted on a table and includes a chin rest and
head band to position the patient’s head properly. With the help of hand-held
lenses, your doctor can also use the slit lamp to examine the retina (the
light-sensitive inner lining of the back of the eye.)
Tonometry
(glaucoma testing)
Tonometry is the name for a variety of
tests that can be performed to determine the pressure inside the eye. Elevated
internal eye pressure can cause glaucoma, which is vision loss due to damage to
the sensitive optic nerve in the back of the eye.
The most common method used for tonometry
is the “air puff” test – where an automated instrument discharges a small burst
of air to the surface of your eye. Based on your eye’s resistance to the puff
of air, the machine calculates the pressure inside your eye – called your
intraocular pressure (IOP).
Though the test itself can be startling,
nothing but air touches your eye during this measurement and there’s no risk of
eye injury from the air puff test.
Another popular way to measure eye
pressure is with an instrument called an applanation tonometer, which is
usually attached to a slit lamp. For this test, a yellow eye drop is placed on
your eyes. Your eyes will feel slightly heavy when the drops start working.
This is not a dilating drop — it is simply a numbing agent combined with a
yellow dye. Then the doctor will have you stare straight ahead in the slit lamp
while he or she gently rests the bright-blue glowing probe of the tonometer on
the front of each eye and manually measures the intraocular pressure.
Like the air puff test, applanation
tonometry is painless and takes just a few seconds.
Since glaucoma is often the result of an
increase of pressure inside the eye, these are important tests for ensuring the
long-term health of your eyes.
Pupil dilation
Your comprehensive exam may include the
use of dilating drops. These medicated eye drops enlargen your pupil so your
doctor can get a better view of the internal structures in the back of the eye. Dilating drops usually take about 20 minutes to
start working. When your pupils are dilated, you will be sensitive to light, because
more light is getting into your eye. You may also notice difficulty reading or focusing
on close objects. These effects can last for up to several hours, depending on
the strength of the drops used.
If you don’t have
sunglasses to wear after
the exam, disposable sunglasses will be provided to help you drive home. Dilation
is very important for people with risk factors for eye disease, because it
allows for a more thorough evaluation of the health of the inside of your eyes.
Summary
These are the most common tests performed
during a standard comprehensive eye exam. Depending on your particular needs,
your doctor may perform additional tests or schedule them to be performed at a
later date.
For more information on eye exams or eye diseases, visit All About Vision®.
Article ©2008 Access Media Group LLC. All
rights reserved. Reproduction other than for one-time personal use is strictly
prohibited.
