Imaging the eye

Laser technology that produces a three-dimensional image of the optic nerve may help ophthalmologists detect the subtle changes that signal the earliest stages of glaucoma. The process, known as confocal scanning laser tomography, is undergoing clinical trials at Yale and the University of California at Los Angeles.

Glaucoma is a condition in which people lose their vision because of abnormally high pressure in the eye. The pressure is the result of fluid buildup caused by blockage in the drainage channel between the back of the cornea and the iris.

"Early detection and appropriate treatment are the only methods of preventing blindness due to glaucoma. Both depend on our ability to analyze the optic nerve to determine if early atrophy is taking place," says M. Bruce Shields, M.D., chair of the Department of Ophthalmology and Visual Science at Yale School of Medicine. His collaborator is Joseph Caprioli, M.D., HS '83, who left Yale last year to become director of the Glaucoma Division of the Jules Stein Eye Institute at UCLA School of Medicine. "There never has been technology sophisticated enough for early diagnosis and careful follow-up," says Dr. Shields. "That is what this laser offers."

The purpose of the Yale-UCLA study is to build scientific evidence confirming that the confocal scanning laser is able to reveal optic nerve damage more accurately than current methods. The scanning laser would aid in screening patients for glaucoma and guiding treatment of those with established disease more precisely. The optic nerve contains nearly a million fibers that send visual signals from the retina to the brain. Although glaucoma encompasses a large group of disorders, the common denominator is gradual deterioration of the optic nerve, leading to blindness.

The visible end of the nerve, referred to as the optic nerve head, may be compared to the eraser end of a pencil, Dr. Shields explains. The nerve extends backward from the eye to the brain, and the portion that can be seen resembles a disc. As nerve fibers die, changes occur in the contour of the optic nerve head. The actual loss of nerve fiber bundles and a posterior deformity—in which the disc bows backward, creating a cup-like malformation—are two changes that may be visible.

During examination with the confocal scanning laser, the patient's head rests in a device similar to a slit lamp, the standard instrument in every ophthalmologist's office. The laser is housed in a camera-like device in front of the patient's eye. The beam is focused on a small portion of tissue in the eye. The reflected light passes through an opening said to be confocal to the laser focus, so that the photodetector "sees" only the small area. The beam scans back and forth across the nerve. Probing deeper with each scan, it completes 32 images of nerve tissue in one second. The laser is attached to a computer, which analyzes data and integrates the images into a three-dimensional model on a monitor.

For more than a decade, beginning in the 1980s, Dr. Shields and Dr. Caprioli corresponded with each other about the separate studies they were conducting in glaucoma. During that time, Dr. Shields was a faculty member at Duke University and Dr. Caprioli was director of the glaucoma service at Yale. They first discussed collaborating on clinical measurements of optic nerve damage in late 1996 and early 1997.

Dr. Shields, who also is chief of ophthalmology at Yale-New Haven Hospital, recently completed a term as president of the American Glaucoma Society. He is author of the Textbook of Glaucoma, now in its fourth U.S. edition. The book has been translated into German, Japanese, Portuguese and Spanish.

Scientists at about a dozen institutions around the world, including Japan and Finland, are conducting research similar to the Yale-UCLA study, says Dr. Shields. "Even though we feel strongly that this new technology does offer something we don't have today," he adds, "we need long-term clinical trials to prove its value."