Glaucoma is sometimes called the silent thief,
slowly stealing your sight before you realize
anything's wrong. The most common form of glaucoma
develops gradually, giving no warning signs. Many
people aren't even aware they have an eye problem
until their vision is extensively damaged.
Screening and diagnosis
If your doctor suspects that you have glaucoma, he or she may perform a
series of tests to detect any signs of damage. Tests include:
Tonometry is a simple, painless procedure that measures your
intraocular pressure. It is usually the initial screening test for
glaucoma. Two common techniques are air-puff tonometry and
applanation tonometry. Air-puff tonometry uses a puff of air to
measure the amount of force needed to indent your cornea. An
applanation tonometer is a sophisticated device that's usually
fitted to a slit lamp. Slit lamps use an intense line of light — a
slit — providing illumination of the cornea, iris, lens and anterior
chamber, and allowing your doctor a good view of these structures.
With tonometry, your doctor numbs your eyes with drops and has you
sit at the slit lamp, where a small flat-tipped cone pushes lightly
against your eyeball. The force required to flatten (applanate) a
small area of your cornea translates into a measure of your
Average normal eye
pressures range from 10 to 21 or 22 millimeters of mercury (mm Hg),
though most pressures are within 14 to 16 mm Hg. Doctors consider
anyone with eye pressure greater than 23 mm Hg to be at risk of
developing glaucoma and in need of careful monitoring for early
signs of glaucoma.
Test for optic
To check the fibers in your optic nerve, your eye doctor uses an
instrument called an ophthalmoscope or biomicroscope, which enables
him or her to look directly through the pupil to the back of your
eye. Your doctor may also use laser light and computers to create a
three-dimensional image of your optic nerve. This can reveal slight
changes that may indicate the beginnings of glaucoma.
To check how your visual field has been affected by glaucoma, the
doctor uses a perimetry test. One method, known as tangent screen
perimetry, requires you to look at a screen with a target in the
center. Your eye doctor or a technician manipulates a small object
on a wand at different locations in your visual field. You indicate
whenever you see the object come into view. By repeating this
process over and over again, your entire visual field can be mapped.
Your eyes are numbed for this test, which uses an ultrasonic wave
instrument to gauge the thickness of each cornea. The thickness of
your corneas is an important factor for accurately diagnosing
glaucoma. If you have thick corneas, your eye pressure reading may
seem high even though you don't have glaucoma. Conversely, people
with thin corneas can have low pressure readings, but have glaucoma.
To distinguish between open-angle glaucoma and angle-closure
glaucoma, your eye doctor may use a technique called gonioscopy (go-ne-OS-kuh-pe),
in which a special lens with an angled mirror is placed on the eye
to inspect the drainage angle. Another test, tonography, can measure
how fast fluid drains through the trabecular meshwork.
To establish a diagnosis of glaucoma, several factors must be present.
These usually include elevated intraocular pressure, areas of vision
loss and damage to the optic nerve. In glaucoma, the optic disk shows
visible signs of damage. The optic disk is the area where all of the
nerve fibers come together at the back of the eye before exiting the
eyeball. An optic disk that has been affected by glaucoma appears
indented, or excavated, as if someone scooped out part of the center of
the disk. This condition is known as cupping. The normal contour and
color of the disk may also be affected by the loss of nerve fibers.
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