Cognitive Demand, Concurrent Viewing Distance, and Digital Eye Strain

Abstract

Purpose: Digital devices are now ubiquitous in modern daily life. Reports of digital eye strain (DES) symptoms are occurring frequently, particularly since the recent COVID-19 pandemic. Despite its prevalence, the mechanisms underlying DES have not been fully elucidated and there is currently no clinically proven treatment. Given that both mental effort and the accommodative and vergence demand have been associated with DES, the purpose of this study was to evaluate the relationship between the cognitive demand of the task, mode of presentation, working distance and symptoms of DES. Method: The study was performed on 30 young, normally-sighted individuals. Each participant completed four trials, each of which included a 30-minute reading task. The four conditions entailed: (1) a cognitively demanding task performed on a digital device (tablet) and (2) a less cognitively demanding task performed on the same digital device. Trials (3) and (4) were identical to (1) and (2) except that the tasks were performed on printed paper. Both prior to and immediately following each 30-minute task, subjects completed a 10 question DES symptom survey. For all four conditions, subjects wore a Clouclip, a spectacle-mounted device which uses infrared technology to monitor the working distance objectively every 5 seconds. Results: While all four 30-minute reading tasks induced symptoms of DES, the increase in symptoms was greater for the cognitively demanding tasks (p= <0.0001). However, there was no significant difference in symptoms between performing the tasks on paper versus the tablet computer (p=0.83). With regard to working distance, there was no difference between the four testing conditions (p=0.11). However, all tasks showed a similar significant reduction in working distance (p=0.001), on average from 32 to 30cm, over the first ten minutes of the task, with the working distance remaining relatively stable after this initial period. Conclusion: These results suggest that cognitive demand plays a greater role in DES than the mode of presentation. In addition, we found no evidence that working distance varies with cognitive demand or the method of presentation. However, it did decrease during the first 10 minutes of each trial. Further work is needed to explain the role of cognitive demand in DES.