New Imaging Device Can Detect Glaucoma Risk
DURHAM, N.C. -- A high-resolution imaging instrument
developed by scientists at Duke University Medical Center can
detect subtle changes in the eye and help identify patients at
risk for glaucoma, decades before the disease does irreversible
Doctors say this high-speed advance in optical coherence
tomography may one day help prevent narrow-angle glaucoma, one
of the major types of a disease considered to be the second
leading cause of blindness in the world.
"We've been talking about treating glaucoma for a long
time," said Sanjay Asrani, MD, an associate professor of
ophthalmology with the Duke Eye Center. "Now we're changing the
paradigm. We want to prevent it."
Dr. Asrani is the lead author of research on this technology
which appears in the June issue of Archives of
Narrow-angle glaucoma is the most serious form of glaucoma,
affecting nearly 500,000 people in the U.S. It can come on
without warning, causing acute painful loss of sight. In a
small percentage of patients, the damage it causes may occur
gradually, but it is difficult to treat and often requires
surgery. Narrow-angle glaucoma is more prevalent among people
with a family history, people who are far-sighted, diabetics,
Doctors measure the angle where the iris and cornea meet
with a test called gonioscopy. The narrower the angle, the
harder it is for the aqueous, or eye fluid, to drain by
following its normal pathway through the Schlemm's canal which
is located at the edge of the cornea. When fluid builds up,
pressure within the eye increases, causing progressive damage
to the optic nerve.
Using a special contact lens that is pressed to the eye,
doctors performing gonioscopy can see if the drain (angle) is
narrow and expected to close in the near future. They can also
determine if it is scarred or abnormally shaped. However,
because the gonioscope lens presses against the eye, it can
make the drain appear open. The same potential for error can
result from the bright light of the microscope used to view the
eye. "It can make the pupil constrict and distort the angle of
the drain," says Dr. Asrani.
In contrast, fourier domain optical coherence tomography
(FDOCT), lets doctors make a 2D, cross-sectional image of the
eye using high-resolution, high-speed beams of light without
any direct contact with the eyeball. "Because it is done with
infrared light spectrum rather than artificial light, we can
check the drain with the room lights on and off to know what
patients experience in real dark and light settings," he says.
"It's also a great tool to show the patients what we are
seeing. They can see how narrow their drain is, and understand
the necessity of preventive procedures such as laser surgery
which can open the drain."
The FDOCT test is not without drawbacks. It cannot look at
the drain from 360 degrees as the gonioscopy can, nor can it
detect new blood vessel growth on the drain. "However, the
knowledge gained by the more sophisticated images may help in
our understanding of what we, as eye doctors, could be
missing," Asrani says.
"We hope this information will make the gonioscopy test more
accurate, and better train ophthalmologists to perform the
test. They should know the ramifications of pressing the
contact lens on the patient's eye, and remember that what they
are seeing under artificial light illumination may not tell the
Just as important are the implications this new imaging
device holds for the future, he says. "This test has improved
our understanding of glaucoma, especially narrow angle, and
opens up the possibility of visualizing changes to the
structures, using different pharmacologic agents and developing
new surgery. It may also assist in obtaining more accurate
diagnosis and provide new areas of treatment."
The co-authors of this study are Marinko Sarunic, PhD,
Cecilia Santiago, MD and Joseph Izatt, PhD.