Objective Evaluation of Visual Fatigue Using Binocular Fusion Maintenance

Abstract

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.

Objective evaluation of visual fatigue in patients with intermittent exotropia

“…BFM is more easily collapsed using binocular stress in patients with IXT than in healthy individuals (Figs 3-5 and Tables 2 and 3). The present findings are in agreement of those reported by Hirota et al [11], who reported that BFM in the healthy volunteers was significantly reduced and fusional vergence range was not significantly different using binocular stress, suggesting that the BFM test can also be applied to patients with IXT.…”

“…The eye position data collected during the 50 s measurement periods were averaged over the three trials before and after the visual task. The binocular fusion break time (T B ) was calculated automatically from the nondominant eye movements based on the results of our previous study [11] using Python 3.6.5. Base min was determined as the average eye position over 2 seconds after beginning the measurement in which the transmittance of the liquid crystal shutter remained equal between the right and left eye.…”

“…The measurement procedure followed the process described in our previous study [11]. The spherical and cylindrical errors in all subjects were corrected between 0.00 D and −0.20 D using objective values obtained from the BWFA at 5.0 m. An examiner asked the subject about the sharpness of the starburst target (33.3 arc minutes) on the printed plate at 33 cm and added plus lenses to both eyes equally until the target could be seen clearly and confirmed that the subject's corrected visual acuity in each eye at 33 cm was equal to or greater than 0.0 logMAR.…”

“…All subjects were asked to complete a subjective symptoms questionnaire at the beginning and end of the examination. The questionnaire was the same as that described in our previous studies (S1 Fig) [11,[21][22][23]). Questions 1-3 [1, How tired are your eyes?…”

“…In our previous work [11], we developed a binocular fusion maintenance (BFM) test for objective determination of visual fatigue. The BFM test has good reproducibility, and BFM scores significantly decrease after a visual task, showing a negative correlation with subjective eye symptom scores.…”