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PurposeIn this study, we investigated whether an individual's visual fatigue can be evaluated objectively and quantitatively from their ability to maintain binocular fusion.MethodsBinocular fusion maintenance (BFM) was measured using a custom-made binocular open-view Shack–Hartmann wavefront aberrometer equipped with liquid crystal shutters, wherein eye movements and wavefront aberrations were measured simultaneously. Transmittance in the liquid crystal shutter in front of the subject's nondominant eye was reduced linearly, and BFM was determined from the transmittance at the point when binocular fusion was broken and vergence eye movement was induced. In total, 40 healthy subjects underwent the BFM test and completed a questionnaire regarding subjective symptoms before and after a visual task lasting 30 minutes.ResultsBFM was significantly reduced after the visual task (P < 0.001) and was negatively correlated with the total subjective eye symptom score (adjusted R2 = 0.752, P < 0.001). Furthermore, the diagnostic accuracy for visual fatigue was significantly higher in BFM than in the conventional test results (aggregated fusional vergence range, near point of convergence, and the high-frequency component of accommodative microfluctuations; P = 0.007).ConclusionsThese results suggest that BFM can be used as an indicator for evaluating visual fatigue.Translational RelevanceBFM can be used to evaluate the visual fatigue caused by the new visual devices, such as head-mount display, objectively.

The purpose of this study was to evaluate the degree of visual fatigue in patients with intermittent exotropia (IXT) using the binocular fusion maintenance (BFM) test. Methods Fourteen patients with IXT (32.1 ± 16.4 years) and 15 age-matched healthy volunteers (31.2 ± 9.3 years) participated in the study. BFM was assessed by measuring the transmittance of liquid crystals placed in front of the subject's nondominant eye at the instance when binocular fusion was broken and vergence eye movement was induced. A questionnaire on subjective symptoms was administered to the subjects before and after the visual task. The visual task consisted of a reciprocal movement between 67 and 40 cm. Results The change [post-pre] of BFM was significantly lower in the IXT group (−0.185 ± 0.187) than in the control group (−0.030 ± 0.070) (P = 0.010). The change of total subjective eye symptom score was significantly greater in the IXT group (2.28 ± 1.43) than in the control group (0.93 ± 1.27) (P = 0.018). The reduction in BFM rate with increasing total subjective eye symptom score was significantly greater in the IXT group (−0.106 ± 0.017) than in the control group (−0.030 ± 0.013) (P = 0.006). Conclusion The present findings objectively showed that patients with IXT are at a greater risk of visual fatigue in comparison with healthy individuals.