One hour of uninterrupted smartphone use reduced blink rate and increased inter-blink intervals in young adults, showing signs of visual fatigue, according to new research.
A study in The Journal of Eye Movement Research observed 30 participants, average age 22 years, as they read e-books, watched videos, and browsed social media reels for 60 minutes each. A portable infrared camera system measured blink frequency, inter-blink intervals, and pupil size throughout the sessions.
Blinking steadily declined across all activities. Rates dropped by 61% during e-book reading, 54% during video watching, and 59% during social media browsing. By the final 15 minutes, participants averaged about 10 blinks per minute compared with more than 17 in the opening 15 minutes.
As blinking decreased, the time between blinks increased. Inter-blink intervals rose by about 40% across all tasks, meaning participants’ eyes remained open longer, which has been linked to discomfort and fatigue.
Pupil size did not change significantly over time but fluctuated more during social media browsing than during reading or video watching. The rapid changes in brightness and content in reels caused continuous adjustments in pupil size, increasing strain on the visual system.
A pre-experiment questionnaire of 110 patients showed that 95% used smartphones for more than two hours daily, and 98% reported use prior to sleep. About 60% experienced mild to severe discomfort following extended use, including eyestrain, neck pain, and hand fatigue. Eighty-three percent reported anxiety, sleep disturbances, or exhaustion. Forty percent used blue light filters or dark mode to lessen discomfort.
Participants in the experiment sat at a fixed distance from the screen in a standardized lighting environment. Each session lasted one hour, and all participants completed the three content types in random order.
“During social media reels, the fluctuation (standard deviation) in values from the average is nearly twice that of reading an e-book or watching videos. It causes higher variation in pupil dilation and inter-blink interval, showing that social media reels’ rapid, dynamic nature strains the eyes more than other types of content,” wrote lead study author Bhanu Priya Dandumahanti of the Department of Computing Technologies, SRM Institute of Science and Technology, Chennai, India, and colleagues.
The study's sample size was small and limited to young adults, most of whom already averaged more than five hours of smartphone use per day. Exposure was restricted to one hour and three content types. The researchers noted that longer durations, larger and more diverse groups, and varied devices would provide a more complete picture of digital eye strain.
The authors reported no conflicts of interest.
Source: Journal of Eye Movement Research