Volume 5, Number 1
Spring, 1996
Plan for Creating a Major
Glaucoma Research Center Moves Forward
"Celebration and Prospect" was the theme of a Foundation luncheon
at the Philadelphia Club on March 13: celebration of the progress
made toward establishing a major glaucoma research center at the
Wills Eye Hospital, and the prospect of taking the next steps
toward meeting that goal.
Foundation President Dr.
George Spaeth, speaking for himself and other members of the Glaucoma
Service present--Dr. Richard Wilson, Dr. Marlene Moster, and Dr.
L. Jay Katz--introduced key elements of the plan. Foremost among
these is that of establishing a Research Professorship in Glaucoma
at Jefferson Medical College.
Dr. Spaeth then introduced
Dr. Alon Harris, "one of the most productive and revolutionary
glaucoma investigators in the world today," as the person the
Foundation hopes to attract to Wills to fill that position. Dr.
Harris addressed his remarks to Foundation Board members Dr. Herman
Goldstine, Robert Bast, Nettie Taylor, and Father Paul Washington;
to Kenneth Moore of Thomas Jefferson University's Development
Office, and to friends of the Foundation present: Ellen Goldstine,
J. Roffe Wike, Stanley and Edna Tuttleman, Jacob Hoffman, Madeline
W.W. King Butcher, Steve Harmelin, Ann Spaeth, Dorothy L. Maloney,
Adele Greene, Samuel Evans, Jane Crosby, David Eastburn, Thomas
Mahon, Berte Stricker, and Frederick Heldring.
Dr. Harris explained that
the major challenge facing glaucoma
investigators is understanding the variety of factors that damage
the optic nerve in primary open-angle glaucoma. Certainly an important
one, and the one most frequently studied, is pressure of the fluid
in the eye too high for the eye to tolerate. But another very
important cause of optic nerve damage in glaucoma that has received
relatively little attention is blood flow to the optic nerve.
It is especially in this area that Dr. Harris is concentrating
his work.
Friend of the Foundation Adele
Green (left) and Board Member Nettie Taylor chat with Dr.
Spaeth after the luncheon.
Kenneth Moore, Vice President for Development, Thomas Jefferson
University (left) and Alon Harris, PhD (right), after the
March 13th luncheon at the Philadelphia Club.
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Lasers: An Important Tool for Treating Glaucoma
by George Spaeth, MD
Patients often prefer up-do-date,
technologically advanced medical treatments. It is easy for glaucoma
patients, for example, to assume that treatment with a laser is
"better" than undergoing surgery with a knife.
It is important for patients
and physicians to remember that treatment with a laser is just
as surgical and just as "invasive" as treatment with a knife.
True, some laser treatments are in fact much safer than almost
any other treatment for glaucoma, including eye drops. Nevertheless,
it is also true that some laser treatments are among the riskiest
treatments for glaucoma. The basic error, as is true for much
of medicine, is the "a rose is a rose is a rose," fallacy. Just
as there is a vast array of roses, some resembling very little
the average person's idea of a rose, so there is also a vast difference
between different types of laser treatments (as there is a vast
difference in the different types of glaucomas). There are a variety
of different lasers used for a variety of different purposes to
treat a variety of different aspects of glaucoma.
In order to understand how
lasers can be used to treat glaucoma, it is necessary to have
some understanding both of how lasers work in general and how
they can be used to affect the eye beneficially.
What is a Laser?
Basically, a laser is a device
that amplifies light by producing light that, unlike light from
ordinary sources, is all one wavelength, that is to say, it is
all exactly one color. Also laser light is said to be "coherent."
This means that the waves or photons, again unlike ordinary light,
are in phase with each other and don't work at cross purposes
with each other. The result is that laser light is extremely intense,
highly directional, and very pure in color (frequency).
Now envision a cylindrical
crystal with mirrors at both ends of the tube. When the light
in the crystal is activated, it bounces back and forth between
the mirrors, and each time it does so, it stimulates more and
more laser light, until the power of the beam inside the crystal
is huge. One of the mirrors is on a pivot and, when activated,
swings out of the way for a millionth or even a trillionth of
a second. When it does, laser light explodes out of the crystal
for one infinitesimally short burst.
Lasers and the Eye
Because these intense narrow
beams of laser light can cut and vaporize tissues in a tiny fraction
of a second without damaging surrounding healthy tissues, they
can be enormously useful in eye surgery. But because they are
so powerful, they also create risks. In general, the risks are
related to the skill of the surgeon and the quality of the equipment
being used. All types of laser treatment can produce serious injury
when misused. Small details are important, such as making sure
that the eyepiece through which the surgeon looks is properly
adjusted for his or her particular refractive error. The lens
that's used to focus the beam at the desired spot must have the
right amount of magnification. The surgeon has to be meticulously
careful that once the target tissue has been penetrated that the
beam doesn't keep going and damage any other tissue.
Different wavelengths of
laser light are produced by different substances, and these different
wavelengths cause different reactions in different tissues of
the eye. The surgeon chooses a laser that produces a specific
wavelength judged best to achieve a certain effect. The major
types of lasers that are used in ophthalmology produce laser light
from argon gas, a neodymium:YAG (yttrium-aluminum-garnet) crystal,
krypton gas, and carbon dioxide gas. The argon laser produces
the shortest wavelength of light routinely used in ophthalmology,
specifically blue light. The YAG crystal produces an even longer
wavelength, in the infrared region.
Using Laser Light to Control
Intraocular Pressure
Now let's see how lasers
can be used to control potentially damaging intraocular pressure
in the eye.
A watery fluid, aqueous humor,
is made by the surface cells of the ciliary body. This fluid circulates
forward into the space behind the iris, the posterior chamber,
over the front surface of the lens, out the hole in the iris (the
pupil), into the space between the cornea and the iris (the anterior
chamber), and leaves the eye by passing out the sieve (trabecular
meshwork), which is just in front of where the iris is in contact
with the wall of the eye.
In the normal eye there's
a balance between the amount of aqueous humor made in the ciliary
body and the amount that flows out through the trabecular meshwork.
When the fluid cannot get out because it is blocked at some place
along that course, the pressure inside the eye (the intraocular
pressure) rises.
Argon Laser Trabeculoplasty
(ALT)
The first laser procedure
to control intraocular pressure we will consider is argon laser
trabeculoplasty (ALT); that is, using argon laser to alter the
shape of the trabecular meshwork, the place where the fluid runs
out of the eye.
The exact mechanism by which
ALT works to lower pressure is not yet understood, but it probably
involves stimulation by the laser beam of chemicals in the trabecular
meshwork that helps to clear the meshwork of debris, and therefore
allows the aqueous humor to flow more easily through it. It may
even encourage repopulation of the meshwork with the normal endothelial
cells, which are lost prematurely in people with open-angle glaucoma.
In an appropriate patient
such as an elderly person with a type of glaucoma in which particles
of unknown composition clog the trabecular meshwork, the likelihood
that argon laser treatment will beneficially lower the intraocular
pressure is around 75%. The duration of the average beneficial
effect averages five years but may be lost within a year; it may,
in some people, last longer than 10 years. The beneficial effect
on intraocular pressure becomes apparent between four and six
weeks following the treatment. The treatment itself is usually
not associated with any symptoms, though there may be a slight
sensitivity to light, a mild redness of the eye, and a minimal
tenderness that lasts for about one week. The treatment is done
as an outpatient, and the person treated can return immediately
to normal activities.
Risks of ALT
Given a proper indication
and a proper technique of performance, the risks of an ALT are
amazingly slight. The major concern is a temporary increase in
intraocular pressure immediately following the treatment that
may last up to about two weeks. Such a rise in pressure is rarely
a concern unless the person having the treatment has an optic
disc that is already badly damaged and which has demonstrated
that it is sensitive to the damaging effects of elevated intraocular
pressure.
Another risk from argon laser
trabeculoplasty relates to the effect of multiple treatments.
Each burn causes a little bit of scarring, and the more marked
the laser power used, the greater the scarring. If high levels
of power are used and the treatment is repeated sufficiently often,
enough of the trabecular meshwork outflow mechanism can become
scarred to cause the pressure to rise.
The comparative risks of
medicinal treatment with drops and laser surgery with argon laser
trabeculoplasty for open-angle glaucoma have been studied by the
National Institutes of Health, with the conclusion that laser
treatment is at least as safe for the eye as the use of eye-drops.
Of course, for the general health of the patient, the laser treatment
is vastly safer, because every type of eye-drop used to treat
glaucoma carries a significant risk for the person's general health.
Laser Peripheral Iridotomy
(LPI)
The other major common procedure
in which a laser is used to treat a patient with glaucoma is the
laser peripheral iridotomy (LPI), in which a tiny hole is made
in the iris where it connects to the inside wall of the eye.
Like ALT, LPI is also done
as an outpatient procedure. It, too, is followed by minimal side
effects, permitting the person to return to work immediately.
However, the duration of the beneficial effect from a peripheral
iridotomy is usually permanent.
The iridotomy is done with
a different type of laser, the Nd:YAG Q-switched laser, in which
the laser beam is meticulously focused just deep to the front
surface of the iris. When the laser is activated, it blasts open
a tiny hole, so small that it usually cannot be seen without a
microscope, but large enough to allow the fluid that has been
trapped behind the iris to move through the hole into the front
of the iris. This equalizes the pressure behind the iris and the
front of the iris and allows the iris to fall back to a position
where it no longer imperils the trabecular meshwork. Where the
iris is not already stuck onto the trabecular meshwork, the likelihood
that a peripheral iridotomy will permanently cure a patient with
a narrow anterior chamber angle is almost 100%.
Complications of LPI
There are two complications
that may occur, even in the right patients, and even with proper
technique; though, again, the frequency of the complications can
be minimized by choosing the right patient and taking appropriate
precautions to lessen the likelihood that the complication would
occur. The first problem is excessive bleeding as a result of
the laser explosion in the iris. The surgeon should select a part
of the iris that appears to be relatively free from blood vessels.
The other problem relates
to the passage of light through the new iridotomy; that is, the
tiny new hole that has been made. The iridotomy should be placed
very close to the 12:00 o'clock position on the eye so that the
hole is underneath the lid. This prevents light from coming through
the hole and eliminates the problem.
The only other risk associated
with an LPI is an elevation of intraocular pressure immediately
after the procedure is completed. The explosion disperses the
iris tissue into the aqueous humor, which floats in the fluid,
getting into and potentially clogging the sieve, the trabecular
meshwork. When the amount of iris dispersed is small, and when
the trabecular meshwork is normal, this usually has no effect
on intraocular pressure. When the amount of tissue is larger and
the trabecular meshwork is abnormal, as it is in some patients
with glaucoma, then the meshwork is temporarily blocked and the
intraocular pressure rises. This increase in intraocular pressure
can almost always be blocked by treating the eye with an agent
that makes the eye make less fluid at the time that the laser
procedure is done.
Support Group to be Organized
Berte Stricker, a patient of Dr. L. Jay Katz of the Glaucoma
Service staff, has volunteered to organize glaucoma patient support
groups in the Philadelphia Metropolitan area. She invites others
who are interested in helping her with this difficult but extremely
important effort to call her at 215-568-0280.
The objectives of these
support groups would be:
- To assist and support those with glaucoma,
their families and friends.
- To educate, inform and help the general
public become aware of glaucoma.
- To assist and/or participate in as many
research activities as possible.
Individuals with a common
"problem" such as glaucoma have found that by coming together,
meeting and discussing their problems, they are able to expand
their personal experiences and understand more about their own
situations. In the case of glaucoma, this is very important!
Glaucoma patients know that
the doctor can only go so far. Living with glaucoma is
beyond what the doctor can do for the glaucoma patient and his/her
family members. An extended "family" is needed to help not only
the person with glaucoma, but also his/her family and friends.
Dr. Spaeth and the other
physicians on the Glaucoma Service at Wills often stress the importance
of glaucoma patients taking ultimate responsibility for their
own health. Becoming a part of this support group initiative is
a wonderful way of affirming the individual patient's own power
to take control of his/her glaucoma. Such an affirmation in itself
cannot help but have a powerful healing effect on the patient's
life.
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