Salzburg Visual Field Trainer (SVFT): A virtual reality device for (the evaluation of) neuropsychological rehabilitation
Authors: Leitner Michael Christian , Gütlin Dirk Christoph , Hawelka Stefan 
Published: March 2021

Objective

So-called “Visual Restitution Therapies” (VRT) claim to ameliorate visual field defects of neurological patients by repeated visual light stimulation, leading to training-related neuroplasticity and resulting in reconnection of lesioned neurons in early cortical areas. Because existing systems are stationary, uncomfortable and unreliable, we developed a training instrument based on virtual reality goggles. The goal of the “Salzburg Visual Field Trainer” (SVFT) is twofold: (1) The device facilitates the clinical evaluation of established neuropsychological rehabilitation approaches, such as VRT. (2) The device enables patients to independently perform VRT based (or other) neuropsychological training methodologies flexibly, comfortably and reliably.

Methods and Analysis

The SVFT was developed on the principles of VRT. Individual configuration of the SVFT is based on perimetric data of the respective patient’s visual field. To validate the utmost important procedure in neuropsychological rehabilitation methodologies - that is displaying stimuli precisely in desired locations in the user’s visual field - two steps were conducted in this proof-of-concept study: First, we assessed the individual “blind spots” location and extent of 40 healthy, normal sighted participants. This was done with the help of our recently developed and validated perimetric methodology “Eye Tracking Based Visual Field Analysis” (EFA). Second, depending on the individual characteristics of every participant’s blind spots, we displayed - with the help of the SVFT - 15 stimuli in the respective locations of every participants’ blind spots and 85 stimuli in the surrounding, fully intact visual area. The ratio between visible and non-visible stimuli, which reflects in the documented behavioral response (clicks on a remote control) of the 40 participants, provides insight into the accuracy of the SVFT to display training stimuli in areas desired by the investigator. As the blind spot is a naturally occurring, absolute scotoma in human vision, we utilized this blind area as an objective criterion and a “simulated” visual field defect to evaluate the (technical) methodology of SVFT.

Results

Outcomes indicate that the SVFT and its methodology is highly accurate in displaying training stimuli in desired areas of the user’s visual field with an accuracy of 99.0%. Data analysis further shows a sensitivity of .980, specificity of .992, positive predictive value of .955, negative predictive value of .996, hit rate of .990, random hit rate of .742 and RATZ-Index of .976. This translates to 14.7% correct non-reactions, 0.7% false non-reactions, 0.3% false reactions and 84.3% correct reactions to displayed test stimuli during the evaluation study with the SVFT. Reports from participants further indicate that the SVFT is comfortable to wear and intuitive to use.

Conclusions

The SVFT can help to investigate the true effects of VRT based methodologies (or other neuropsychological approaches) and the underlying mechanisms of training-related neuroplasticity in early regions of the visual cortex in neurological patients suffering from visual field defects.