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-
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."