Prototype visual field test allows for objectivity, shorter test times

Issue: October 2005

ByJennifer Byrne

Harry J. Wyatt, PhD [photo]
Harry J. Wyatt

A new visual field test that provides non-contact, objective measurements and shorter testing times is currently in the early stages of development. Tentatively called the Shaped Stimulus Test, this prototype system was created by Harry J. Wyatt, PhD, a professor at the State University of New York College of Optometry.

“Many older glaucoma patients really hate visual field tests,” Dr. Wyatt said. “This test is fast and easy, and you don’t have to push any buttons or make any judgments.”

Origin of the test

Dr. Wyatt said his test is primarily based on the pupillary light reflex, which has been used by clinicians for years to assess the status of the pathway from the retina to the brainstem.

“You’ve only got the one pupil, so when it contracts, it doesn’t tell you a lot of detail. It just tells you some light has hit the retina,” he told Primary Care Optometry News.

Dr. Wyatt said that it is possible to glean more information from the pupillary light reflex. “The retina and the system that drives the pupil in that reflex will add up light from all over the whole visual world, essentially the entire visual field of the eye,” he said. “I have been doing this on and off for a number of years with the pupil. I noticed years ago that if you stimulate the pupil with a pair of stimuli presented alternately, the system was very sensitive to the balance of potency of the two stimuli.”

How it works

Dr. Wyatt said the test consists of a pair of stimuli, with the entire set of stimuli consisting of three pairs. “If you were to put them all up there at once, they would fill a larger part of the visual field,” he said. “You actually just put one pair up there at a time. The pair of stimuli is symmetric at the horizontal. The one below the horizontal is the mirror image of the one above the horizontal.”

Dr. Wyatt said the shapes of these stimuli were crafted to capture territories that are especially likely to be damaged by glaucoma. “In one trial, you take one of the pairs and present it. You turn the upper one on, it goes off. You turn the lower one on, it goes off,” he said. “You do this for one second each. The pupillometer is steadily measuring and recording pupil diameter during this. The whole thing lasts 18 seconds.”

During this time, the patient’s only task is to look at a fixation mark in the shape of a red cross, Dr. Wyatt said. “We indicate that it would be nice if they didn’t blink a whole lot, but we can live with two or three blinks,” he said. “They don’t have to push any buttons or say anything.”

Altogether, Dr. Wyatt said, the test takes about 2 minutes. So far, he has gotten very positive patient responses, he said. “We’ve often come to the end of testing, and the patient will say, ‘That’s all?’” he said.

Challenging conditions

Dr. Wyatt said there may be some conditions that could potentially interfere with his visual field test. One such condition is a captured haptic, which would involve an IOL that has been displaced from its normal position.

“This is not common. If it prevented the pupil from responding to light, it would prevent the test from being carried out,” he said.

Dr. Wyatt said it would be possible for a cataract to also affect the test. “If it were very dense, it might not be possible to carry it out,” he said. “However, in general, the presence of a cataract would have less effect on the pupil-based test than it would on standard visual field testing. The very large stimuli would not be as affected as the small test stimuli used in visual fields.”

Dr. Wyatt said he has also examined the effect of blur, as in the case of an uncorrected patient, on the test. “Up to 6 D of blur had very little effect,” he said.

A prototype system

At the present time, Dr. Wyatt said this technology is not yet commercially available. “I’m working with a prototype system now that we put together from available equipment,” he said. “It’s very impractical as it is. I’m trying to put together a more compact version that would be halfway between this and something marketable.”

As a scientist, Dr. Wyatt said he does not have the time or the resources to produce and market the product on his own. “I’ve had some talks with some people in industry, and they are interested,” he said.

Dr. Wyatt said other objective techniques are currently available, but unlike his perimeter, these usually require the placement of an electrode on the patient. “They are not widely in use at this point,” he said. “They tend to take a long time, and they tend to be rather demanding on the patient, in terms of being absolutely still.”

He said although his visual field test was put together with existing technology, the equipment is being used in a new way. “The concept behind it and the way the pieces are integrated is new,” he said.

For Your Information:

Harry J. Wyatt, PhD, is a professor of biological sciences at the SUNY College of Optometry. He can be reached at 33 West 42nd St., New York, NY 10036; (212) 780-5163; fax: (212) 780-5174; e-mail: hwyatt@sunyopt.edu.