ROSSLYN, Va., February 22, 1999---Gaze directly at the red spot of light from David Hunter's little black box, and the box will start beeping. The instant you look away, the beeping stops. Look back at it, and the sound resumes.
The box---a retinal birefringence scanner---measures the eyes' point of fixation in a new way independent of the head's position or other factors. By this method, doctors may be able to diagnose eye diseases in infants and children too young to cooperate with a physician's exam. Disabled people could use the device to communicate or operate appliances from anywhere in a room.
"It's a new way to use eye contact to replace a remote control," said Hunter, M.D., Ph.D., assistant professor of ophthalmology and biomedical engineering at the Johns Hopkins University. "There are other methods that use eye position for remote control, but they are based on video, which requires a camera to focus, so the subject's head position is fairly restricted.
"The scanner has the potential to give more freedom of movement to the person, because it depends on the focus of the person's eyes and not of the camera. As long as light is getting into the eye and back out to the scanner, it works," he said.
Hunter has a clinical practice at Hopkins and regularly sees young eye patients. He and colleague David Guyton, M.D., developed the scanner to help diagnose amblyopia early enough to cure it. They led a group of researchers at the Laboratory of Ophthalmic Optics in the Krieger Children's Eye Center at Hopkins' Wilmer Eye Institute.
Amblyopia, or lazy eye, affects about 5 percent of the population, causing slight to severe vision impairment. In the disorder, one eye is either misaligned or out of focus, causing a faulty signal to reach the brain. To compensate, the brain responds by closing off the signal from the weaker eye. Over time, this can prevent the problem eye from ever focusing sharply, even with corrective lenses.
But caught early, amblyopia can be corrected completely by having the patient wear a patch over the stronger eye for six months or more until the weaker one develops equal strength.
"I deal with this from the clinical side every day," Hunter said. "It's frustrating to see a child at 6 or 7 and not be able to do anything for them. Had they been seen at age 3, I could have completely treated them."
The retinal birefringence scanner---named for its ability to detect changes in reflected light---works like this: The shoebox-sized scanner emits a faint, red circular beam of polarized, infrared light. Polarized light waves are all aligned, unlike normal light waves, which go in all directions.
When a person looks into the red light, the beam is reflected back to a set of detectors that can tell whether the aligned waves have been disturbed. Polarized light reflected from the fovea, the point of fixation on the retina, is disturbed in a unique way. This distortion indicates that the eye is looking at the red light. Light reflected from other parts of the eye is not distorted in the same way.
The device has been tested in patients, but hundreds of additional tests in patients of all ages and sizes will be necessary before the device could be put into clinical practice. The scanner is described in the March issue of the journal Applied Optics, and preliminary patient results will be presented at the April meeting of the American Association for Pediatric Ophthalmology and Strabismus.
If the scanner continues to perform well in patient trials, other applications may emerge. In glaucoma visual field testing, for example, patients are required to focus on a spot during the examination. The clinician must check the patient during the exam to be sure the eye remains fixed on the spot, otherwise the test is inaccurate. Hunter's scanner could guarantee that patients are looking where they should throughout the glaucoma test.
"The scanner is still in the lab; it is not a commercial instrument," Hunter said. "The distance from the lab to a commercial product can become infinitely far."
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