Giving the Side-Eye: Asymmetrical Response of the Tear Film Margins to Lateral Gaze Changes

Background: Lateral eye movements are part of natural ocular motility, and their effect on tear film behavior is largely unknown because they are usually not evaluated during tear film examinations, where patients are required to look straight ahead. This study aimed to determine what happens to the tear film during lateral eye movements in the absence of blinking. Methods: Tear film dynamics during a sequence of open-eye lateral gaze maneuvers were recorded using an infrared camera system (TearView). Results: The study included 15 healthy participants (5 female; median age 26) who had no ocular surface-related complaints. It was observed that lateral eye movements exposed new ocular surface areas not previously covered by the tear film. The tear film margins reacted to lateral eye movements by spreading towards the newly uncovered ocular surface areas, thereby recoating them. This response was asymmetrical, with a tear reservoir in the lacus lacrimalis of the medial canthus providing additional tear film spread only during ocular abduction. Conclusions: These findings expand our understanding of tear film physiology beyond static gaze. They might also bear implications for dry eye disease and oculoplastic surgical techniques affecting the medial canthus.