Researchers in India found one hour of smartphone use reduced blink rate and increased inter-blink intervals in young adults, with short social media videos (reels) causing greater pupil fluctuations than e-book reading or long-form video watching.  

Researchers from SRM Institute of Science and Technology, Chennai, and Singapore University of Technology and Design reported the findings in the Journal of Eye Movement Research. The team developed a portable, wireless eye-activity measurement system using a Raspberry Pi and infrared camera to track blink rate, inter-blink interval and pupil diameter during one-hour smartphone sessions. They studied 30 adults with a mean age of 22.6 years who had used smartphones for more than one year and who averaged 5.3 hours per day of use. 

From the first 15 minutes to the last 15 minutes of use, average blink rate fell by 61% for e-book reading, 54% for video watching and 59% for social media, while inter-blink interval rose by 42%, 39% and 42%, respectively. The authors said blink rate and inter-blink interval changed significantly over time, while pupil diameter did not significantly change with duration. 

However, pupil fluctuations were greater during reels viewing, which the researchers attributed to rapidly changing brightness and content in reels. They concluded this dynamic visual input may place more strain on the eyes than more stable screen activities such as reading or watching videos.