Stimulating a region of the brain for 20 minutes with a mild electrical current may improve vision for about two hours, and those with worse eyesight see the most improvement, a new study has found.
"This kind of stimulation can improve cognitive processing in other brain areas, so if we stimulate the visual system, could we improve processing?" said Geoff Woodman, associate professor at the Vanderbilt University in the US.
"Could we make someone's vision better - not at the level of the eye, like Lasik or glasses, but directly at the level of the brain?" said Woodman.
Twenty young, healthy subjects with normal or near-normal vision were asked to evaluate the relative position of two identical vertical lines and judged whether they were perfectly aligned or offset.
The test is more sensitive than a standard eye chart, and gave the researchers a very precise measurement of each subjects' visual acuity.
The researchers then passed a very mild electric current through the visual cortex, the area at the back of the brain that processes visual information.
After 20 minutes, the subjects were asked to perform the test again, and about 75 per cent showed measurable improvement following the brain stimulation.
The researchers performed several variations of this experiment to test the effects of different intensity levels, current directions and electrode placements.
This third experiment confirmed that the electrodes had to be positioned specifically over the brain's visual processing centre in order to affect the subjects' eyesight.
They also measured how the stimulus changed the speed with which the brain processed visual information and whether the stimulation also improved the subjects' contrast sensitivity - their ability to differentiate between shades of grey.
The contrast experiment was notable because they found that the stimulation only improved contrast sensitivity at frequencies also associated with visual acuity, indicating that it was just the subjects' visual acuity that was being affected, not the contrast sensitivity.
Lead author Robert Reinhart, from the Boston University who conducted this research as a PhD student at Vanderbilt, said this finding had interesting implications for future basic science.
For their last experiment, the researchers wanted to see if the improvement they saw in the first experiment was significant enough to translate into a real-world task - reading a standard eye chart.
They found that the stimulation effects improved the subjects' vision by an average of one to two letters, though there was significant variation between subjects.
"We saw that those who came in with poorer vision, who might be on their way to needing glasses, had these big leaps, while others who came in with excellent vision showed no change," Reinhart said.
The study was published in the journal Current Biology.
