The refresh rate is supported by the frame rate of the software that runs the simulation.
Expressed in FPS, or frames per second, it refers to how often the software can generate an update for the screen. Higher frame rates improve the sense of immersion and reduce indices of simulator sickness.
The biggest factors that affect FPS are the complexity of the simulation and the quality of the graphics processing hardware hooked up to the HMD. A poor balance of complexity and hardware capability can introduce visual and audio slowdowns and stutters.