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A mismatch between the interpupillary distance (IPD) and inter-optical system distance (IOSD) in virtual reality (VR) applications can lead to discomfort. The IOSD must be adjustable according to the user's IPD to solve this issue. In this study, we investigate IPD estimation methods by tracking eye movements such as conjugate eye movement (CEM) and vergence. We hypothesize that the distance between the two pupils maintained during the CEM and is identical to the IPD. The vergencebased method induces eye divergence and determines the IPD as the maximum distance between pupils. Experiments with visual stimuli to induce CEM and divergence were conducted. The average errors of the estimated IPDs for the CEM-based and vergence-based methods were 2.06 and 1.30 mm, respectively. Furthermore, the analysis results show that the proposed methods can effectively reduce the IPD-IOSD difference and are especially helpful for users with a small IPD. If the IOSD is adjusted to the IPD estimated by the proposed methods, then VR discomfort can be eliminated.INDEX TERMS Eye movement, head-mounted display (HMD), interpupillary distance (IPD), IPD measurement, virtual reality (VR) device.

Peripheral dimming technique based on gaze tracking was proposed to reduce the power consumption of emissive displays adopted in headset. This technique divides an image into two zones: a central zone which is a circular area centered on the gaze point, and a peripheral zone which is the outer area of the central zone. This technique achieves power savings by gradually reducing the brightness in the peripheral zone while maintaining the brightness of the central zone. This paper investigates effects of central zone size (CZS) on the technique under a wide field of view (FoV) environment. Psychophysical experiments are conducted to determine the threshold dimming conditions for the CZSs of 10°, 25°, and 40°. The results showed that the individual variations and the mean value of threshold dimming condition increased in proportion to CZS. Interestingly, in contrast, the power-saving efficiency depending on the CZS was not significantly different. The technique can reduce power consumption of display panel by approximately 12% on average, up to 15%. It is demonstrated that the technique is feasible even in a wide FoV environment, and the CZS can be flexibly determined depending on the application or image content.INDEX TERMS Peripheral vision, low-power technique, self-luminous displays, head-mounted display devices