EYE FATIGUE WHEN VIEWING BINOCULAR DISPLAYS: EFFECTS OF MISMATCH BETWEEN ACCOMMODATION AND VERGENCE

This paper reports an experiment conducted to investigate the levels of eye fatigue caused by viewing stereo images on a binocular display with compatible and incompatible lens focuses. Twelve participants watched four 30-minute stereoscopic slide shows under four viewing conditions that were exhaustive combinations of two levels of lens focus (40 cm and 200 cm) and stereo depths (40 cm +/- 0.3 dioptres and 200 cm +/- 0.3 dioptres). Five Landolt C rings would appear at a pre-determined depth on each slide and participants would locate the opening of the centre ring. Rated levels of eye fatigue were taken every two minutes. Results show that when using a binocular display of 200 cm lens focus, viewing stereo images with incompatible stereo depths (40 cm) as compared to compatible depths of 200 cm significantly increased the rated levels of eye fatigue (p<0.001, F(1,383) = 33, ANOVA). This carries serious implications to the manufacturers of binocular displays with fixed lens focus of 200 cm. Contrary to previous assumption, adjusting the lens focus of the displays to 40 cm to match images with a stereo depth of 40 cm did not result in significant reduction in eye fatigue (p > 0.5, F(1,383) = 0.36, ANOVA). The lack of benefits had been due to an opposite confounding effects of accommodation on eye fatigue. Data also indicate that when the confounding effect of accommodation was in agreement with the compatibility effects between lens focus and stereo depth (i.e., a change of lens focus from 40 cm to 200 cm to match images of stereo depths of 200 cm), very significant reduction in rated levels of eye fatigue were reported (p < 0.001, F(1,383) = 55.5, ANOVA).