TESTS IN GLAUCOMA
When Glaucoma is suspected or diagnosed, a
variety of tests are used to determine the extent of
the disease. Visual field is probably most
commonly used tool. Some tests are only helpful
in evaluating the type of glaucoma such
Gonioscopy. Here are some of the common tests
used in glaucoma evaluation.
- Visual fields
- Nerve Fiber Layer Analyzer
- Pachymetry
- Gonioscopy
- Disc Photos
- Fluorescein Angiography ( only in
neovascular glaucoma to find the cause)
EXAMPLES OF VISUAL FIELDS IN GLAUCOMA
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A normal looking visual field
There are no dense scotomas
or blind spots on this test
A superior field defect,
most probably caused by
glaucoma in suspected or
diagnosed case. Optic
nerve appearance should
co-relate with this field
Superior and inferior
defects. This case is more
advanced and may need
aggressive approach to
save the remaining tunnel
vision
This field shows very
advanced case, almost
end stage. Some cases
may continue to reach
stage like this despite
treatment
PERIMETER OR VISUAL FIELD ANALYZER
Visual field testing or simply side vision testing is done in medicine in numerous conditions, such as neurology and brain disorders but in ophthalmology this test is used most in the diagnosis and management of glaucoma. There are numerous manufacturers out there producing excellent pieces of equipment but Humphrey Field Analyzer is probably most used machine in the US. This test can be done in several modes such as screening but a threshold test is more desirable since it does more in depth analysis but also takes more time. Even a threshold test does not pick up very early damage from glaucoma.
The visual field test is used to assess any damage to peripheral vision and if any defect is found then rest is repeated periodically to see if the progression of glaucoma has been arrested. If a subsequent test shows worsening of the field defect, then more aggressive treatment may be needed.
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GONIOSCOPY
Gonioscopy is evaluation of the drainage angle of the eye and is done in
the office by the examining physician using the slit lamp and a contact lens
generally called gonioprism.
In Glaucoma cases it is important to know the anatomical structure of the
eye, specially the draining area, space between Iris and the Cornea. This
area or the angle as it is called should be adequately open to allow free
flow of Aqueous Humor or fluid inside the eye. In some cases this space
may be narrow or shallow and flow of Aqueous Humor may be impeded.
Sometimes a small opening in the Iris using a laser may be necessary to
keep the angle open.
The angle is also evaluated for other factors which can effect the pressure
in the eye, such as synechia ( scarring and adhesions), pigment on the
surface of the Trabecular Mesh work ( blocking the drainage) or presence
of blood vessels ( a key factor in neovascular type of glaucoma)
SLIT LAMP AND GONIOPRISM
DIAGRAM OF AN EYE WITH ANGLE
( SPACE BETWEEN CORNEA AND IRIS ) WIDE
OPEN AND FLUID SHOULD FLOW FREELY
ON THE RIGHT ANGLE IS VERY NARROW OR
ALMOST CLOSED
PHOTOGRAPH OF A VERY
NARROW ANGLE
EYE TREATED WITH IRIDOTOMY
( SMALL OPENING IN THE IRIS ) BY
A LASER TO FACILITATE FLUID
CIRCULATION
PHOTOGRAPHY OF THE OPTIC NERVE HEAD
( DISC PHOTOGRAPHS)
SERIAL PHOTOGRAPHS OF THE OPTIC NERVE HEAD ARE VERY VALUABLE TOOL IN THE MANAGEMENT OF GLAUCOMA.
VERY SMALL CHANGES IN THE CENTRAL CUP OR CHANGES IN THE NERVE FIBER BUNDLES OR EVEN SMALL HEMORRHAGES COULD EASILY BE MISSED BY NAKED HUMAN EYE BY WHEN SERIAL PHOTOGRAPHS ARE COMPARED, SUCH MINUTE CHANGES CAN BE PICKED UP AND TREATMENT COULD BE ADJUSTED ACCORDINGLY
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SOME EXAMPLES OF
THE OPTIC NERVE
CHANGES OVER TIME
IN GLAUCOMA
PACHYMETRY
Pachymetry is measurement of corneal thickness and is done using an ultrasound machine called "Pachymeter". Thickness of the cornea can effect the intra ocular pressure measurement and therefore it is usually checked in the beginning and pressure readings are adjusted accordingly.
Since the corneal thickness does not change through out life, unless person had a refractive surgery like LASIK, test is done only once.
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NERVE FIBER LAYER ANALYZERS / OCT
In the treatment or suspected cases of glaucoma a very common test is used to look at health of the optic nerve. Optic nerve is a little over a millimeter in thickness and conveys images from the retina to the brain. Though very small in diameter, the optic nerve has over a million fibers packed inside it. These instruments, Optic Nerve Fiber Analyzers, use scanning laser technology to look at the thickness and health of these nerve fibers. These instruments are very precise and are extremely valuable in the management of glaucoma. Tests may be repeated periodically to assess status of the optic nerves and progression of the disease. There are several different instruments of this kind available today. Our office uses two of them, GDX and OCT, which are almost a standard today in the management of glaucoma.
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A look at GDX report Left side shows extensive nerve fiber layer loss, right side is normal.
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Moderate nerve fiber loss on GDX and
associated loss of peripheral vision
Examples of normal vision and gradually constricting visual fields in glaucoma. We are born with a
very wide field of vision but glaucoma starts to damage our field of vision and it shrinks starting at
the periphery and vision gradually leads to " tunnel vision" which is the last part to go, leading to
total blindness.
St. Louis STL
3535 S. Jefferson, Suite S-4
Saint Louis, MO 63118
Phone 314-771-3000