Human eye movements for vision are remarkably adaptable

Our eyes are constantly on the move, darting this way and that four to five times per second. Now researchers have found that the precise manner of those eye movements can change within a matter of hours. This discovery by researchers from the University of Southern California might suggest a way to help those with macular degeneration better cope with vision loss.

"The system that controls how the eyes move is far more malleable than the literature has suggested," says Bosco Tjan of the University of Southern California. "We showed that people with normal vision can quickly adjust to a temporary occlusion of their foveal vision by adapting a consistent point in their peripheral vision as their new point of gaze."

The fovea refers to the small, center-most portion of the retina, which is responsible for our high-resolution vision. We move our eyes to direct the fovea to different parts of a scene, constructing a picture of the world around us. In those with age-related macular degeneration, progressive loss of foveal vision leads to visual impairment and blindness.

In the new study, MiYoung Kwon, Anirvan Nandy, and Tjan simulated a loss of foveal vision in six normally sighted young adults by blocking part of a visual scene with a gray disc that followed the individuals' eye gaze. Those individuals were then asked to complete demanding object-following and visual-search tasks. Within three hours of working on those tasks, people showed a remarkably fast and spontaneous adjustment of eye movements. Once developed, that change in their "point of gaze" was retained over a period of weeks and was reengaged whenever their foveal vision was blocked.

Tjan and his team say they were surprised by the rate of this adjustment. They note that patients with macular degeneration frequently do adapt their point of gaze, but in a process that takes months, not days or hours. They suggest that practice with a visible gray disc like the one used in the study might help speed that process of visual rehabilitation along. The discovery also reveals that the oculomotor (eye movement) system prefers control simplicity over optimality.

"Gaze control by the oculomotor system, although highly automatic, is malleable in the same sense that motor control of the limbs is malleable," Tjan says. "This finding is potentially very good news for people who lose their foveal vision due to macular diseases. It may be possible to create the right conditions for the oculomotor system to quickly adjust," Kwon adds.