Simulated Hemianopia Reveals Right Hemifield Reading Difficulties

A simulated reading environment can reveal eye movement pattern changes associated with hemianopia, enabling researchers to investigate strategies to improve hemianopic field loss following a stroke, according to a study published in Vision Research. These simulated environments showed slower reading speeds and a higher number of saccades among individuals with right homonymous visual field defects (HVFD) compared with individuals experiencing left HVFD, according to the report. 

Researchers enrolled 30 individuals in the investigation and stratified them according to age. The team included 2 cohorts — 1 consisting of  young adults (n=15; mean age, 20.9 years) and another consisting of adults aged 40 to 70 years (n=15; mean age, 54.7 years) to account for reading ability changes that occur with age. Individuals aged 40 to 70 years were also selected on the premise that 97% of estimated stroke incidence occurs over the age of 40, according to the report. Participants from both groups read passages from the International Reading Speed Test from a monitor while investigators tracked monocular eye position and movements with an eye tracker. 

The team conducted a total of 3 reading trials. The first trial simulated no vision loss (control) and did not include any image blurring. The remaining trials simulated right and left HVFD which involved blurring text to the right and left side of the screen, respectively, with filters. 

Reading behavior under the control condition involved a repeating staircase pattern in which the participant would fixate on a word for a short period, promptly move to the next word, and demonstrate a large displacement after reaching the end of the line and beginning a search for the new line (approximately − 200 to +200  pixel coordinates).

Both simulated right and left HVFD conditions produced slower reading speeds, a higher number of forward saccades per line, and lower median forward saccade amplitudes compared with reading under controlled conditions, the report shows. Individuals with a simulated right HVFD demonstrated slower reading speeds (124 vs 197 words per minute; P <.001), a greater number of forward saccades per line (7.68 vs 5.95; P <.001), and lower median forward saccade amplitudes (1.32 vs 1.70; P <.001) compared with participants with a simulated left HVFD. Both hemianopic simulations produced a significantly higher number of saccades during the return sweep compared with the controlled condition (right: 1.78 vs left: 1.27 vs control: 0.28; P <.001). 

Reading speed was slowed more significantly in the right hemifield in both the older and younger cohorts, but the younger group was more affected by the loss of visual information, the report shows. A loss of 0.1 cycles per second on the right side resulted in a loss of 29.1 words per minute in the younger group compared with a loss of 16.5 words per minute in individuals aged 40 to 70 years. 

“The methods presented here for measuring the critical cut-off for reading speed have some potentially interesting implications for restitutive strategies in the blind field of stroke survivors,” according to researchers, “This study seeks to act as a starting point to explore the effects of partial visual restoration on reading with hemianopia and other forms of vision loss.”

Study limitations include a limited sample size and the use of simulated conditions.