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

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

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.


Barry Skarf (416)598-6133
Moshe Eizenman (416)978-5523