Objective Evaluation for Relationship between Visual Fatigue and Tear Film Stability in Smartphone Use

Purpose: To investigate whether tear film instability induces visual fatigue, we used the binocular fusion maintenance (BFM) test and non-invasive tear film break-up time (NI-BUT). Methods: Eleven young adult volunteers (age [mean ± standard deviation], 20.7 ± 1.4 years) participated in this study. BFM was assessed by measuring the transmittance of liquid crystals placed in front of the subject’s non-dominant eye when binocular fusion was broken, and non-dominant eye was shifted to heterophoric. The NI-BUT was determined using the distortion of the Meyer ring. The volunteers were administered the BFM, NI-BUT, and subjective symptom questionnaire before and after a 30-minute visual task. Results: BFM (pre vs. post: 0.95 ± 0.09 vs. 0.75 ± 0.16) was significantly lower in the post-visual task than in the pre-visual task ( P  = 0.012). NI-BUT (9.12 ± 1.00 s vs. 5.69 ± 3.11 s) was significantly shorter in the post-visual task than in the pre-visual task ( P  = 0.011). Total subjective eye symptom (2.91 ± 0.79 vs. 5.45 ± 2.02) was significantly greater in the post-visual task than in the pre-visual task ( P  = 0.012). The change in BFM (− 0.20 ± 0.18) was significantly and positively correlated with the change in NI-BUT (− 3.43 ± 3.19) ( R 2  = 0.385, P  = 0.042) and was significantly and negatively correlated with the change in total subjective eye symptom score (2.54 ± 2.23) ( R 2  = 0.470, P  = 0.020). Conclusion: The findings suggest that tear film instability induces visual fatigue objectively.