The purpose of this study was to develop and validate RetinaVR, an affordable, portable, and fully immersive virtual reality (VR) simulator for vitreoretinal surgery training. We built RetinaVR as a standalone app on the Meta Quest 2 VR headset. It simulates core vitrectomy, peripheral shaving, membrane peeling, and endolaser application. In a validation study (n = 20 novices and experts), we measured: efficiency, safety, and module-specific performance. We first explored unadjusted performance differences through an effect size analysis. Then, a linear mixed-effects model was used to isolate the impact of age, sex, expertise, and experimental run on performance. Experts were significantly safer in membrane peeling but not when controlling for other factors. Experts were significantly better in core vitrectomy, even when controlling for other factors (P = 0.014). Heatmap analysis of endolaser applications showed more consistent retinopexy among experts. Age had no impact on performance, but male subjects were faster in peripheral shaving (P = 0.036) and membrane peeling (P = 0.004). A learning curve was demonstrated with improving efficiency at each experimental run for all modules. Repetition also led to improved safety during membrane peeling (P = 0.003), and better task-specific performance during core vitrectomy (P = 0.038), peripheral shaving (P = 0.011), and endolaser application (P = 0.043). User experience was favorable to excellent in all spheres. RetinaVR demonstrates potential as an affordable, portable training tool for vitreoretinal surgery. Its construct validity is established, showing varying performance in a way that correlates with experimental runs, age, sex, and level of expertise. Fully immersive VR technology could revolutionize surgical training, making it more accessible, especially in developing nations.

Psychophysiological indicators have garnered significant interest in the assessment of presence. However, despite this interest, the nature of the relationship between psychophysiological indicators and presence factors remains undetermined. Presence, the perceived realness of a mediated or virtual experience, is modulated by two factors: immersion and coherence. Immersion represents the extent and precision of the simulated sensory modalities, while coherence refers to the environment's ability to behave as expected by the user. To study the relationship between psychophysiological indicators and presence factors, we objectively manipulated immersion by altering three visual qualities. The visual qualities were set to values above, at, or below their functional threshold. These thresholds are defined as a perceptual boundary under which a sensory quality value should be considered functionally degraded. Sixty participants performed a driving task in a virtual environment under the aforementioned conditions, while we measured their cardiovascular and eye responses. We found that degraded immersion conditions yielded significantly different psychophysiological indicator results than the condition without degradation. However, we observed an effect of immersion degradation on our measured variables only when the visual conditions were set below the functional threshold. Manipulations of immersion below the functional threshold introduced unreasonable circumstances which modified our participants' behavior. Thus, our findings suggest a direct impact of immersion on coherence and highlight the sensitivity of psychophysiological indicators to the coherence of a virtual environment. These results have theoretical implications, as a presence concepts relationship model should include the direct impact of immersion on coherence.

We consider that to objectively measure immersion, one needs to assess how each sensory quality is reproduced in a virtual environment. In this perspective, we introduce the concept of functional threshold which corresponds to the value at which a sensory quality can be degraded without being noticed by the user of a virtual environment. We suggest that the perceived realism of a virtual experience can potentially be evoked for sensory qualities values ranging from the perceptual threshold to the functional threshold. Thus, the identification of functional thresholds values allows us to constrain immersion. To lay the foundation for the identification of functional thresholds, we applied a modified version of the method of limits. We measured the value at which 30 participants were able to identify the degradation of their field of view (FOV), visual acuity, and contrast sensitivity while executing a multidirectional selection test. This enabled us to identify functional perceptual thresholds of 96.6 degrees for FOV, 12.2 arcmin for visual acuity, and 25.6
% for contrast sensitivity.

Abstract Despite the growth in research and development in the area of virtual reality over the past few years, virtual worlds do not yet convey a feeling of presence that matches reality. This is particularly due to the difference in visual perception of flat images as compared to actual 3D. We studied the impact of two parameters of the stereoscopic configuration, namely, the inter-camera distance (ICD) and the presence of a depth of field blur (DOF blur). We conducted an experiment involving 18 participants in order to evaluate this impact, based on both subjective and objective criteria. We examined six configurations which differed in the presence or absence of {DOF} blur and the value of the ICD: fixed and equal to the anatomical interpupillary distance, fixed and chosen by the participant, or variable, depending on the depth of the viewer's point of regard (POR). The {DOF} blur and variable {ICD} require the use of an eye tracking system in order to be adjusted with respect to the POR. To our knowledge, no previously published research has tested a gaze-contingent variable {ICD} along with dynamic {DOF} blur in a Cave Automatic Virtual Environment. Our results show that the anatomical and variable {ICD} performed similarly regarding each criterion of the experiment, both being more efficient than the fixed ICD. Besides, as with earlier similar attempts, the configurations with {DOF} blur obtained lower subjective evaluations. Although mainly not significant, the results obtained by the variable {ICD} and {DOF} blur are likely due to a noticeable delay in the parameters update. We also designed a new methodology to objectively compare the geometry and depth rendering, based on the reproduction of the same scene in the real and virtual setups, and then on the study of resulting ocular convergence and angular deviation from a target. This leads to a new comparative criterion for the perceptual realism of immersive virtual environments based on the visual behavior similarity between real and virtual setups.

Scoliosis is a complex deformation of the spine requiring, in severe cases, a highly delicate and invasive surgical instrumentation operation to correct the spinal deformities. Available traditional tools for surgical training have major drawbacks for which virtual reality (VR) technologies and computer simulation can offer solutions. In this paper, we introduce a surgical simulator integrating a complex patient-specific biomechanical model into a VR immersive environment in a collaborative context, the first of its kind for scoliosis surgery training. We present the results for the fully collaborative AVE (audio visual environment) aspects of the simulator. Haptic forces are computed in the biomechanical model, but not yet available as a haptic feedback because of the high forces and torques characteristic of scoliosis surgery, requiring the use of a specifically designed haptic device (in progress). Transatlantic collaborative tests showed that, with our simulator, users on different continents can train collaboratively for scoliosis surgery and visualise the forces and the resulting correction. With the eventual addition of haptic devices, they will also be able to feel the forces remotely. ©2008 IEEE.

In this paper we present Wolverine, a simple scene-graph library that incorporates advanced concepts such as node and object differentiation, seamless serialization for distributed environments, and multimedia elements including dynamic textures and video sources. By examining the specifics of Wolverine, we will compare our approach to other scene-graph APIs and dwell on its use in a videoconferencing shared-reality collaborative application. © 2005 by the Massachusetts Institute of Technology.