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U of T professors devise better way to test sight in babies
In a darkened room at Toronto's Hospital for Sick Children, a baby, its
head dotted with electrodes, sits in its mother's lap and watches flashing
black and white checkerboards and stripes on a television screen. Soon
after the test, doctors will know if the child can see and how well it can
see.
The testing procedure, which involves measuring brain wave activity
prompted by visual stimuli (also called visual evoked potentials or VEP's)
has been perfected by Drs. Barry Skarf of the Department of Ophthalmology
and Moshe Eizenman of U of T's Institute
Their procedure is more accurate than tests used elsewhere because
Eizenman has developed a novel, real-time computer program to extract
brain wave responses from extremely small patterns (similar in size to the
bottom line of a standard eye test) which produce much more reliable
results. Until now, doctors would have to extrapolate the baby's ability
to see small stimuli from test results using large stimuli. "In Effect,
Dr. Eizenman has developed a way of looking at brain waves that is more
sensitive than methods previously available, " says Skarf.
At the HSC, VEP's are used in a number of clinical applications: to
determine whether a visual problem is cognitive; to assess whether babies
who don't appear to see well will see better in the future; to determine a
course of treatment for such problems in which one eye turns in or is
weaker than the other eye. The second aspect of the researchers' work
involves the development of a stimulator for stereopsis, or binocular
vision, which is the fusing of images from both eyes into one picture that
has depth. "The problem with testing binocular vision, " explains Skarf,
"is that most stimuli presented to young children have other cues that
can be seen with one eye alone. We wanted to devise stimuli that can only
be seen by both eyes together and would produce specific brain waves to
the stimuli."
Based on a binocular stimulus invented by an American researcher, Eizenman
had developed a stimulus that generates a pattern on a tv screen which
looks like distortion (a snow storm) when viewed with only one eye, but
when viewed through special glasses with both eyes emits a distinctive
three-dimensional pattern.
Skarf and Eizenman are now testing binocular VEP's on young children. They
are examining children with normal sight and evaluating eye function in
children with visual disorders. This is the first test of binocular vision
to be carried out with large numbers. "Using this binocular stimulus with
the very sensitive detector system for analyzing responses, we hope to
have a system which will allow us to test binocular vision in young babies,
quickly and easily, and to measure responses in a better way than before."
In addition to this clinical research, Skarf now wants to direct his
attention to some basic research questions about the development of vision.
"We are interested in more than just developing tools. We want to know how
binocular vision develops and which factors interfere with development. We
want to find out what wheels turn in the brain to produce lazy eyes and
impaired binocular vision."
Skarf and Eizenman receive funding from the Medical Research Council of
Canada.
CONTACT:
Barry Skarf (416)598-6133 Moshe Eizenman (416)978-5523
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