  Current gaze input methods for VR headsets predominantly utilize the gaze ray
as a pointing cursor, often neglecting depth information in it. This study
introduces FocusFlow, a novel gaze interaction technique that integrates focal
depth into gaze input dimensions, facilitating users to actively shift their
focus along the depth dimension for interaction. A detection algorithm to
identify the user's focal depth is developed. Based on this, a layer-based UI
is proposed, which uses focal depth changes to enable layer switch operations,
offering an intuitive hands-free selection method. We also designed visual cues
to guide users to adjust focal depth accurately and get familiar with the
interaction process. Preliminary evaluations demonstrate the system's
usability, and several potential applications are discussed. Through FocusFlow,
we aim to enrich the input dimensions of gaze interaction, achieving more
intuitive and efficient human-computer interactions on headset devices.
