Exercise-Induced Changes in Tear Film Physiology and Tear Biomarkers: A Narrative Review

Introduction: The tear film functions as a dynamic interface, adapting its volume, stability, and osmolarity to systemic and environmental stress. Exercise produces simultaneous autonomic, hemodynamic, metabolic, thermal, and fluid-balance effects, making tear fluid a potentially informative, but methodologically challenging matrix for research. Methods: A structured literature search of PubMed was performed and included articles published between January 2014 and August 2026. Human studies evaluating acute exercise, habitual physical activity, or exercise interventions in relation to tear secretion, tear-film stability, osmolarity, inflammatory mediators, oxidative-stress markers were prioritized. Animal studies and methodological literature on tear biomarkers analysis were included for context. Results: Aerobic exercise generally increases tear secretion and can improve tear-film stability, whereas strenuous exercise accompanied by fluid loss may transiently increase tear osmolarity. Tear cytokine concentrations often decline after exercise, and reduced tear 8-hydroxy-2′-deoxyguanosine has been reported in dry-eye populations. However, several tear proteins and lipids show no immediate change. Fitness status, hydration, environmental exposure, blinking, sampling technique, and post-exercise timing substantially modify observed responses. Conclusions: Exercise alters both tear-film dynamics and selected tear biomarkers, but the response is not uniformly beneficial or detrimental. The seemingly contradictory effects of exercise may account for the variability in current findings. While aerobic activity can stimulate lacrimal secretion and exert systemic anti-inflammatory effects, exercise-associated dehydration and environmental exposure may increase tear hyperosmolarity and evaporation, thereby compromising tear-film stability. Standardized protocols and longitudinal biomarker studies are required before tears can be used for exercise monitoring or clinical decision-making.