A virtual reality headset displays a three-dimensional (3D) virtual scene and includes a varifocal element to dynamically adjust a focal length of an optics block included in the virtual reality headset based on a location in the virtual scene where the user is looking. The headset tracks a user's eyes to approximate gaze lines and determines a plane of focus for a frame of the virtual scene as the intersection of the gaze lines. The varifocal element adjusts the focal length of the optics block so the optics block is focused at the plane of focus, which keeps the user's eyes in a zone of comfort as vergence and accommodation change. Based on the plane of focus, the virtual reality headset may provide depth cues, such as depth of field blur, to planes in the virtual scene deeper in the user's field of view than the plane of focus.