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.

Here, we study a low-power technique for displays based on gaze tracking, called peripheral dimming. In this work, the threshold levels of the lightness reduction ratio (LRR), where people notice differences in brightness, depending on gaze positions and image brightness, are investigated. A psychophysical experiment with five gaze positions and three image brightness conditions is performed, and the estimated threshold levels are obtained. To investigate the significance of the differences between the threshold levels, the overlap method and the Bayesian estimation (BEST) analysis are performed. The analysis results show that the difference of the threshold levels depending on the conditions is insignificant. Thus, the proposed technique can operate with a constant LRR level, regardless of the gaze position or image brightness, while maintaining the perceptual image quality. In addition, the proposed technique reduces the power consumption of virtual reality (VR) displays by 12–14% on average. We believe that the peripheral dimming technique would contribute to reducing the power of the self-luminous displays used for VR headsets with an integrated eye tracker.

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