IN stimuli (also called visual evokedpotentials or

IN BABIES In a darkened room at Toronto’s Hospital forSickChildren, a baby, its head dotted with electrodes, sits in itsmother’s lap and watches flashing black and white checkerboardsand stripes on a television screen. Soon after the test, doctorswill know if the child can see and how well it can see.The testing procedure, which involves measuring brain waveactivity prompted by visual stimuli (also called visual evokedpotentials or VEP’s) has been perfected by Drs.

Barry Skarf ofthe Department of Ophthalmology and Moshe Eizenman of U of T’sInstituteTheir procedure is more accurate than tests used elsewherebecause Eizenman has developed a novel,real-time computerprogram to extract brain wave responses from extremely smallpatterns (similar in size to the bottom line of a standard eyetest) which produce much more reliable results.Until now,doctors would have to extrapolate the baby’s ability to seesmall stimuli from test results using large stimuli. “In Effect,Dr. Eizenman has developed a way of looking at brain waves thatis more sensitive than methods previously available, ” saysSkarf.

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At the HSC,VEP’s are used in a number of clinicalapplications:to determine whether avisualproblemiscognitive; to assess whether babies who don’t appear to see wellwill see better in the future;to determine a course oftreatment for such problems in which one eye turns in or isweaker than the other eye. The second aspect of the researchers’work involves the development of a stimulator for stereopsis, orbinocular vision, which is the fusing of images from both eyesinto one picture that has depth.”The problem with testingbinocular vision, ” explains Skarf,”is that most stimulipresented to young children have other cues that can be seenwith one eye alone.

We wanted to devise stimuli that can only beseen by both eyes together and would produce specific brainwaves to the stimuli.”Based on a binocular stimulus invented by an Americanresearcher, Eizenman had developed a stimulus that generates apattern on a tv screen which looks like distortion (a snowstorm) when viewed with only one eye, but when viewed throughspecial glasses with both eyes emits a distinctive three-dimensional pattern.Skarf and Eizenman are now testing binocular VEP’s onyoung children. They are examining children with normal sightand evaluating eye function in children with visual disorders.This is the first test of binocular vision to be carried outwith large numbers. “Using this binocular stimulus with the verysensitive detector system for analyzing responses,we hope tohave a system which will allow us to test binocular vision inyoung babies, quickly and easily, and to measure responses in abetter way than before.

“In addition to this clinical research, Skarf now wants todirect his attention to some basic research questions about thedevelopment of vision. “We are interested in more than justdeveloping tools. We want to know how binocular vision developsand which factors interfere with development. We want to findout what wheels turn in the brain to produce lazy eyes andimpaired binocular vision.

” Skarf and Eizenman receive funding from the MedicalResearch Council of Canada. CONTACT:Barry Skarf(416)598-6133Moshe Eizenman (416)978-5523

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