Effects of ambient illuminance and mobile phone screen brightness on tear film stability, visual fatigue, and blink patterns during reading.

Purpose: This study aimed to investigate the impacts of different ambient illuminance and screen brightness conditions on tear film stability, visual fatigue, and blink patterns during mobile phone reading.

Methods: This prospective study involved 30 young subjects who completed 4 experiments based on ambient illuminance and screen brightness: Group 1: bright room, bright screen; Group 2: dark room, dark screen; Group 3: bright room, dark screen; Group 4: dark room, bright screen. Participants completed a 30-minute mobile phone reading task in each experiment. Tear film stability indicators, including fluorescein tear break-up time (FTBUT), noninvasive tear breakup time, tear meniscus height, and lipid layer thickness, were measured before and after reading. During reading, an infrared camera recorded blink-related parameters. Subjective questionnaires assessed comfort and visual fatigue.

Results: After the reading task, the FTBUT of each group significantly decreased (all P < 0.05). Notably, all tear film stability indicators significantly changed in Group 4. The incomplete blink rate in all the groups tended to increase over time (all P < 0.05). Among the four groups, Group 4 had a significantly greater incomplete blink rate and partial blink ratio (P < 0.05), along with a greater subjective fatigue score, than did Group 1 (P < 0.01). The frequency of incomplete blinks (r = 0.29, P = 0.03) was positively correlated with the visual fatigue score.

Conclusions: Reading in a dark environment with a bright screen led to the most significant instability of the tear film, visual fatigue, and changes in blink patterns. Therefore, it is advisable to avoid reading under such conditions.