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How is glaucoma
diagnosed?
Since the treatment
methods for open angle and angle closure glaucoma are different,
it is important to identify the mechanism involved. The diagnosis
(or exclusion) of glaucoma requires a detailed and comprehensive
eye examination. Your doctor will do the following examinations:
To detect glaucoma your doctor will do the following examinations:
-
a routine
vision test that requires reading letters from a chart,
-
Slit lamp
(microscope) examination: This special microscope is the
ophthalmologist's stethoscope and all patients, not just
those suspected of having glaucoma, must undergo a slit
lamp examination.
-
The pressure
inside the eye is measured with an 'applanation tonometer'
attached to the slit lamp. A hand held version of the
instrument is also effective. It may be necessary to obtain
multiple readings of the pressure during the course of
the day and at night. The older method of resting an instrument
on the cornea while the patient lies down is not accurate.
The newer non-contact air soft (computerized) instrument
may be good for screening but cannot be used for diagnosis
or treatment of glaucoma.
-
An examination
of the angle of the eye is done with the help of a gonioscope.
This is a contact lens placed on the eye to examine the
angle of the eye. Its use is mandatory in determining
the type of glaucoma - open angle or angle closure.
The above two
steps require the use of drops to eliminate the sensation
in the eye. The drops may burn a little bit.
- An optic disc examination
on a dilated eye is also required. The doctor will usually
instill eye drops to dilate the pupil to facilitate examination
of the optic disc and the back of the eye, the retina. For
obtaining a stereoscopic view on the microscope a hand-held
lens or a contact lens is the best method. A computerized
scan of the optic disc may also be done.
- To confirm the diagnosis,
the doctor will conduct an automated field or perimetry
test. Damage to the optic nerve limits the field of vision,
but regular vision, i.e. the ability to read an ophthalmologist's
eye chart, is affected at a much later stage. In its early
stages glaucoma can only be detected or monitored by using
an automated perimetry test. A normal patient will have
a 'full field vision', while a person with glaucoma has
black, non-seeing areas in the field of vision.
Many people have difficulty
doing the perimetry test at first, and may be better at it
the second or the third time. Baseline tests are necessary
for future comparison and periodic examinations are essential
to check the progression of the disease.
Considering the importance of the test, ANY automated perimeter
is NOT acceptable. The field test is a subjective test and
it is important to have a calibrated machine with an appropriate
normal database against which to compare your results.
Sometimes a diagnosis may not be possible on one visit. In
very early cases it may be necessary to repeat the entire
examination after a period of observation.
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