10, 11 Although ergonomic recommendations aim at reducing postural related symptoms arising from prolonged computer use, as far as we know, they do not consider the relationship between display position and ocular surface exposure. As for tablets, e-books, and other handheld devices such as smartphones, they are usually viewed in inferior gaze, similar to traditional printed reading material, and at a shorter distance, although user preferences also may vary. In contrast, laptop users have been observed to place their devices in a variety of positions, 10 usually opting for a lower position, compared with desktop computer users. 9 It may be noted that ergonomic recommendations for these devices suggest that the center of the display should be placed slightly lower than the horizontal line of sight. First, ocular exposure, which results in tear film evaporation, 8 is influenced by actual screen position, and is more relevant for desktop computers. 7 Several factors may account for the differences in visual fatigue among reading platforms.
Visual fatigue among VDT users was first documented by Hultgren and Knave in 1974, 6 with symptoms increasing toward the end of the day. However, only electronic reading resulted in an increase in the percentage of incomplete blinks, which may account for the symptoms experienced by VDT users. The high cognitive demands associated with a reading task led to a reduction in SEBR, irrespective of type of reading platform. The percentage of incomplete blinks was found to increase when reading was conducted on an electronic platform, in contrast to hard-copy text. Video analysis was subsequently conducted to assess blink parameters.Īll reading conditions resulted in a decrease in SEBR when compared with baseline conditions (all P < 0.001), with the least negative impact corresponding to reading in a 330% expanded display. Texts were presented in electronic (tablet and computer display at 100% and 330% zoom levels) and hard-copy (text in book position in silence and aloud and text pasted on the computer display) formats. Face video recordings were captured while participants observed in silence a landscape picture at 2 m (baseline) and during six different, 6-minute controlled reading experimental conditions. All participants had good ocular health and reported no symptoms of dry eye (OSDI score < 15). To evaluate spontaneous eye blink rate (SEBR) and percentage of incomplete blinks in different hard-copy and visual display terminal (VDT) reading conditions, compared with baseline conditions.Ī sample of 50 participants (29 females, age range, 18–74 years) were recruited for this study.
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