The Eye Examination for Glaucoma
There are many different types of glaucoma, each with
its own particular features. The eye examination allows
your doctor to determine to determine
whether you have glaucoma and, if you have it, to determine
the type. If you
already have glaucoma, the examination shows whether it
is stable or worse. With a thorough examination, your
doctor is better able to monitor and treat your glaucoma.
This article will help you better understand the eye examination
and why various tests are performed.
Patient Interview
Before actually examining your eyes, your doctor will
ask you questions about your general health, medical conditions,
and prior eye problems. It is
important to provide accurate information as well as a
listing of all medications (both tablets and eye drops)
that you are using.
Visual Acuity
The first step in the eye examination is to assess your
vision. Your ability to see sharply at a distance or up
close for reading is referred to as visual acuity. Your
visual acuity is measured by having you read an eye chart
(Figure 1). If you have |
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Figure 1. A tandard eye chart for measuring visual
acuity is familiar to almost everyone. |
glasses
to see better at a distance, your vision is usually
checked with you wearing them. A patient with 6/6
vision is one who can see objects at 6 meters that
a healthy individual also sees at 6 meters. If your
visual acuity is less than 6/6, you then will be
checked to determine whether it can be improved
with a new pair of glasses. This process is called
refraction (Figure 2). During refraction, different
sets of lenses are placed in front of each eye to
determine which ones give you the best vision. The
entire process is performed twice, once for each
eye. Also, it may be done again to improve your
reading vision.
Glaucoma decreases your visual acuity only when
it is moderately advanced. In addition to glaucoma,
decreased visual acuity may result from other conditions
such as macular degeneration, diabetes, cataracts,
or certain eye drops used to treat glaucoma, such
as pilocarpine.
Pupil Examination
The pupils are examined to determine whether the
visual pathway from the eye to the brain is intact
and functioning. If you look in a mirror at the
coloured portion of |
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Figure 2. During refraction, different sets of
lenses are placed in front of each eye to determine
which ones give you the best vision.
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Figure 3. The pupil is visible as a black circle
in the centre of the iris. With a bright light,
the pupil is small (a). With dim lighting, the pupil
widens to allow more light to enter the eye (b).
The pupil returns to a smaller size when bright
light is restored (c). |
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your eye, known
as the iris, you will see a small black area located at
its centre. This region is called the pupil.
Normal shrinking of the pupil to light and opening in
the absence of light indicate that the visual pathway
from the eye to the brain is intact and still working
(Figure 3). A comparison of the light response of the
two pupils may reveal that the visual pathway in one or
both eyes is damaged.
In glaucoma, the optic nerve is damaged and the visual
pathway does not function normally. Therefore, the response
of the pupil to light may be abnormal.
In addition to glaucoma, other optic nerve diseases, prior
eye injury or surgery, and certain medications also can
affect the response of the pupil to light. Certain medications
used to treat glaucoma affect the muscles influencing
pupil size, and your pupil may not react at all.
Slitlamp Examination
Slitlamp examination is an extremely important part of
the eye examination and is usually performed at each visit.
The slitlamp is a type of magnifying glass or microscope
that is used to examine the living eye. It is also known
as a biomicroscope. During the slitlamp test, you are
asked to place your head on a chinrest, and a magnified
view of the eye is examined. The light beam that illuminates
the eye is a thin slit, which gives your doctor a good
view. Slitlamp examination is rapid and easily performed
(Figure 4). The slitlamp is used to diagnose many eye
diseases. Since many of the structures of the eye (such
as the lens and cornea) are normally clear, the inside
of the eye can be seen quite well. |
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Figure 4. The slitlamp biomicroscope is indispensable
for the careful examination of the eye (a). The
slitlamp allows small white flecks to be seen on
the surface of the lens in this patient with pseudoexfoliation
and glaucoma (b). |
Slitlamp
examination assists your eye doctor in determining
the type of your glaucoma. We now know that there
may be over 50 different types of glaucoma, each
of which has a characteristic treatment. For example,
small white flecks on the lens of the eye may be
indicative of a type of glaucoma known as pseudoexfoliation
(Figure 4b): a common condition in Scandinavian
and Mediterranean countries. Your doctor may also
be able to detect inflammation within the eye as
a cause of your high eye pressure.
Tonometry
Measurement of eye pressure follows the slitlamp
examination. This test, also known as tonometry,
is important in the assessment of glaucoma because
eye pressure may be the single most important factor
that affects the course of the disease. Its accurate
measurement is therefore essential. |
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To measure eye
pressure, an anaesthetic drop is placed on the eye. The
drop briefly stings and, within a few seconds, the surface
of the eye is temporarily numbed. Eye pressure can then
be measured with a device known as a tonometer
(Figure 5). For this measurement, the tip of the tonometer
is gently placed upon the eye. You may feel it near your
eyelashes. This procedure is quick, reliable and painless.
Seeral other methods of measuring eye pressure are sometimes
used. One of these, an “air puff ” tonometer,
is less accurate, but eye drops are not required. |
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Gonioscopy
Once the surface of the eye has been numbed, it
becomes possible to perform gonioscopy (Figure 6a).
By gently placing a special contact lens on the
eye, your doctor can examine the drain within the
eye to help determine the type of glaucoma.
Using the slitlamp for magnification, your doctor
can determine whether the drain is open or closed,
check its colour, and see if scar tissue is present
(Figure 6b). You might feel slight pressure on the
eye as your doctor moves the lens, but this should
not be uncomfortable. Gonioscopy is usually done
annually, although there may be more frequent examinations
with certain forms of glaucoma or use of certain
medications.
Pupil Dilation
Since the optic nerve is damaged in glaucoma, it
is important for your eye doctor to carefully
examine the back of the eye (where the optic nerve
is located). The optic nerve is best examined after
the pupils are enlarged with eye drops. Some individuals
experience a mild blurring of vision, glare from
bright lights, or difficultly reading for as long
as 6 hours following pupil dilation.
Optic Nerve and Nerve Fibre Layer Examination
Examination of the optic nerve is essential to detect
glaucoma or determine whether glaucoma damage is
stable (Figure 7). Progressive change in the appearance
of the optic nerve indicates that the disease is
worsening. If the appearance of the optic nerve
is unchanged, this indicates that the glaucoma is
most likely stable and under control.
Although a hand-held instrument, known as an ophthalmoscope,
can be used, the use of the slitlamp with a special
lens allows a threedimensional examination of the
optic nerve.
Your doctor observes the optic nerve and assesses
its shape and colour. Most doctors draw a picture
in the patient’s chart for future reference.
In addition, photographs of the optic nerve may
be obtained. Future examinations of the optic nerve
can then be compared to the initial drawing or photographs
to detect changes in shape or colour. This is an
examination that should be performed at least once
or twice yearly.
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Figure 5. Measurement of eye pressure being performed
with the tonometer. The blue light aids in the measurement.
Figure 6. Gonioscopy allows your doctor to examine
the drain within the eye. A special contact lens
is placed over the eye (a). Through the lens, your
doctor examines the trabecular meshwork (arrow),
which drains aqueous fluid (b).
Figure 7. The optic nerve as seen during examination
by your doctor. |
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Retina Examination
Many other diseases besides glaucoma can cause loss of
vision or damage to the optic nerve or the surrounding
retina. A variety of techniques, most of which use a bright
light, allow yur doctor to examine almost every aspect
of your retina.
Visual Field Testing
The term visual field refers to the entire area you can
see while looking at a fixed location. For example, while
watching a stoplight, you might notice a car
pulling up beside you in the next lane. Your peripheral
vision enables you to see the movement of the car. The
visual field is large when both eyes are working properly.
With glaucoma, the field of view is often reduced. The
visual field is measured using an instrument called a
perimeter.
If you have glaucoma and some loss of visual field is
present, your condition will be followed carefully with
repeated testing to determine whether the problem has
been halted or if further loss is occurring. The time
interval between visual field tests depends on many different
factors and is best determined by your eye doctor. Regular
examinations are very important for the proper management
of
your glaucoma. |
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Summary
The eye examination is essential for the proper diagnosis
and treatment of glaucoma. Each of the various components
of the examination, which are summarised on page 7, provides
your eye doctor with information that allows you to receive
the best possible care.
Author: Jeffrey M. Liebmann, M.D.
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