Published: June 9, 2008
Updated: June 10, 2008
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By Duke Medicine News and Communications
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 damage.
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 Ophthalmology.
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, and Asians.
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 whole story."
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.