Cognitive demand, concurrent viewing distances, and digital eyestrain

Digital devices are ubiquitous in modern daily life. Although a high prevalence of digital eyestrain has been reported, the mechanisms underlying digital eyestrain have not been fully elucidated, and there is currently no proven treatment.

This study aimed to evaluate the relationship between the cognitive demand of a near task, mode of presentation (digital or paper), working distance, and symptoms of digital eyestrain.

Thirty young participants completed four 30-minute reading tasks. The four conditions (performed in randomized order) entailed (1) a cognitively demanding task performed on a tablet computer and (2) a less cognitively demanding task performed on the same device. Trials (3) and (4) were identical to (1) and (2) except that the tasks were performed on paper. Subjects could hold the reading task at any distance they felt comfortable. Before and immediately following each task, subjects completed a digital eyestrain symptom survey. For all four conditions, a spectacle-mounted device (Clouclip) was used to measure the working distance objectively.

Although all four tasks induced significant symptoms, there was a significant difference between the four conditions, with the increase being greatest for the cognitively demanding task on the tablet computer. There was no significant difference in working distance for the four conditions, and all tasks showed a similar reduction in working distance (p=0.001), on average, from 31.6 to 28.9 cm, over the first 10 minutes, with the working distance remaining stable after this initial period.

Task-induced symptoms varied with both cognitive demand and mode of presentation. However, working distance did not vary significantly with these factors. The wording distance decreased during the first 10 minutes of each trial and was markedly closer than 40 cm for all conditions. The closer working distances being adopted should be considered during routine clinical testing.