Abstract
Purpose :
Patients with homonymous hemianopia (HH) report difficulty detecting and keeping track of objects in the blind hemifield, and some HH patients have great difficulty adjusting to their impairment. Here we compare scan patterns in HH patients with those in normally sighted, age-matched controls, for 3 different visual activities that are challenging for HH patients.
Methods :
Patients with HH and controls were recruited through the Low Vision, neuro-ophthalmology, and stroke services of Johns Hopkins Medicine and came in for up to 6 visits over 12 months. All 9 HH subjects recruited have left HH with >70%loss of the blind hemifield. Here we report results from a standardized paragraph reading test (IReST); a comparative visual search (CVS) test, in which the subject had to identify the single mismatched object pair in two otherwise identical sets of 20 objects to the left and right of fixation; and a random dot counting (RDC) test, in which 10 – 14 white dots were displayed on a dark background. All three tests were presented in a head-mounted display with built-in gaze (pupil and head) tracking.
Results :
As expected, gaze patterns in HH showed impairment in all leftward saccades, i.e., those into the blind hemifield; rightward saccades were indistinguishable from those in controls. In IReST, initial saccades to the start of the left line were indistinguishable in duration (120±20 ms) from those in controls, but showed a systematic undershoot followed by 4-8 small leftward saccades to reach the start of the next line (see figures). This, more than actual word reading, accounted for the 80% slower overall reading speed in HH. In CVS, leftward saccades were similarly broken up, leading to a 50% slower average response time. In RDC, leftward scan patterns in HH tended to be erratic in early trials, becoming more regular over time.
Conclusions :
Scan patterns in HH differ from those in controls in predictable and systematic ways. We are following our subjects and seeking to enroll patients with recent (< 1 month) occipital stroke to study the development and possible adjustment of scan patterns in HH, with the goal of developing rehabilitation strategies.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.