Hemianopic field loss (HFL)—loss of half of the field of vision in one eye—can occur after stroke or traumatic brain injury (TBI) and can severely impact basic visuomotor tasks, such as pointing and computer use. It can also affect a person’s ability to communicate normally through mutual gaze. That is to say, those affected by HFL often can’t make eye contact with another person. This can occur in either eye, but new research published in Optometry and Vision Science shows that when it happens in the left eye, patients have a harder row to hoe than when it happens in the right.

Researchers looked into the cases of 22 HFL patients, 13 with loss in their left eyes and nine with loss in their right, as well as 17 controls. All participants were evaluated in a single session wherein they underwent line bisection and gaze performance testing. They were also asked to rate their difficulties with social interaction due to gaze perception issues.

In gaze-direction evaluations, the judgments of participants with right HFL were all within the same range as the control group. But, for the left HFL, the investigators saw a wide variability between subjects, much wider than that for participants with right HFL. There were three participants with left HFL without neglect whose mean direction of straight-ahead gaze fell outside the range of normal vision; one of these participants judged straight-ahead gaze to be further to the right, and two judged it to be further to the left. All four participants with left HFL and neglect history made straight-ahead gaze judgments that were outside the range of normal vision, and all were to the right of true straight-ahead by a median of 3.9 degrees.

The participants with left field loss, especially those with neglect history, had greater difficulties than individuals with right HFL in compensating for low-level spatial biases (as manifested in line bisection) and when performing the more complex, higher-level task of judging gaze direction.