Princeton Weekly Bulletin September 28, 1998
Computer therapy restores sight
By Mary Caffrey
A specialized regimen of computer therapy can restore some vision loss due to brain injuries caused by stroke or trauma, according to visiting Research Scientist Bernhard Sabel, who is spending a year in the Department of Psychology. Until now, this type of vision loss has been considered untreatable.
Sabel and colleagues conducted an experiment at the University of Magdeburg Medical School in Germany, in which adult patients who had suffered a stroke or brain trauma and lost major portions of their field of vision were able to regain an average of five degrees of the field. (This is the equivalent of half a page of a standard magazine held at arm's length.) On average, patients improved their vision between 30 and 70 percent above baseline, and some patients who had lost their ability to read regained it. Members of a control group did not achieve similar results.
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According to Sabel, the use of a computer as a therapeutic tool to treat blindness is also significant. "It is noninvasive, and it has no side effects," he said. Because the test subjects can do the computer therapy at home, it is cost-effective and compliance is extremely high: of 38 therapy and control group patients, only one (a member of the control group) dropped out of the study.
Brain plasticity
"I've always been interested in how the brain repairs itself," said Sabel, who received his PhD from Clark University and was a postdoctoral fellow at Massachusetts Institute of Technology. "When we get a cut on our skin and it heals, no one thinks anything of it. But people don't think the brain can repair itself, yet it does."
When vision loss occurs after a brain injury, many cells are destroyed, but some number of the hardiest cells survive, Sabel explained. These "survivor cells" offer the potential for restored vision. With proper stimulation, these cells undergo dramatic change.
Experiments with animals have shown that up to 70 percent of normal vision can be achieved with only 10 percent of the cells, according to Sabel. The key is to provide focused stimulation. "If you're practicing a difficult passage on the piano for a half-hour by just banging he keys, you will not learn to play well. If, however, you concentrate on the same piece and play it over and over, you will learn to play it well."
In Sabel's experiment, the computer targeted the "transition zone" in each test subject's vision field, which is located between the field with intact vision and the area where vision was completely lost. In this area of partial vision are cells that have survived the injury. These "islands of residual vision" allow patients to see some stimuli, while others go unseen. Getting patients to focus on this transition zone offers the best hope of restoring the vision field, Sabel said, because the repetitive activation of the surviving cells strengthens their synaptic connections.
Experiment design
The 38 patients in the restitution therapy and the control groups were assessed to identify their transition zones. They were then given instructions in their respective training regimens. Patients in the therapy group were required to focus on a fixation point on their computer screens and then asked to hit a computer key when they saw stimuli, which appeared as white dots on the computer screen. To ensure their continued focus on the fixed point, test subjects also had to hit a key when the fixed point changed colors. Patients in the control group, by contrast, were asked to respond to stimuli only in one irrelevant location on the screen.
Both groups contained some test subjects who had suffered damage to the optic nerve, which connects the retina to the brain, as well as those with injury in higher cortical areas. These postchiasmatic injuries involve vision loss in both eyes and are considered more serious.
By monitoring how often the patients receiving the restitution training correctly hit the keyboard after viewing stimuli, researchers could periodically adjust the regimen for each patient, pushing the stimuli farther and farther out into the patient's blind area. Thus, the transition zones for these patients increased or moved over time, continually enlarging their visual fields.
Vision improved after only a few weeks of computer training. After six months, vision tests recorded improvements for 95 percent of the patients in the restitution therapy group, with 78 percent of the subjects stating that they had noticed a change themselves. Patients who had experienced optic nerve damage benefited from the training more than those with postchiasmatic injury. In the control group, only a few of the optic nerve patients recovered any of their visual field, and none with postchiasmatic injuries saw improvement. Only 16 percent of the control subjects reported improved vision.
Although it is suspected that an individual patient's results will vary depending on the nature of the injury, "We are not yet able to predict who profits the most" from the therapy, Sabel said. "But the findings clearly show that partial blindness is not as irreversible as generally believed. Vision can, in fact, be restored to a significant degree."
The article by Erich Kasten, Stefan Wust, Wolfgang Behrens-Baumann and Sabel appeared September 1 in Nature medicine.