RESULTS

The literature search produced 6,592 citations. A total of 43 studies met the inclusion criteria. After excluding studies of poor quality (score≤ 14), 42 studies, representing 44 experiments (n= 620) were finally included. Seven (15.9%) experiments treated post-traumatic stress disorder (PTSD), and seven (15.9%) treated fear of flying. Five (11.4%) experiments treated panic disorder with agoraphobia, fear of heights, and social anxiety disorder. Three (6.8%) experiments treated spider phobia, and two (4.5%) treated claustrophobia, psychotic disorders, vestibular disorders, and amblyopia. One (2.2%) experiment treated dental phobia, eating disorders, depression, and autistic spectrum disorder. The median sample size was 12 (3–58), and the median of the mean age of the sample size was 35.6 years (8.7–63.5 years). The number of intervention sessions ranged from 1 to 60, and intervention duration ranged from 1 to 16 weeks. The results indicated that the use of HMDs led to significant improvement in patient outcomes for the treatment of PTSD (SMD= 0.61, 95% CI= 0.41 to 0.82, p< 0.001), fear of flying (SMD= 0.55, 95% CI= 0.34 to 0.77, p< 0.001), panic disorder with agoraphobia (SMD= 0.53, 95% CI= 0.27 to 0.79, p< 0.001), fear of heights (SMD= 0.70, 95% CI= 0.31 to 1.10, p< 0.001), and social anxiety disorder (SMD= 0.40, 95% CI= 0.18 to 0.63, p< 0.001). No significant improvement in patient outcomes was observed for spider phobia (SMD= 0.35, 95% CI=-0.45 to 0.75, p= 0.083), claustrophobia (SMD= 0.64, 95% CI=-0.08 to 1.36, p= 0.079), psychotic disorders (SMD= 0.12, 95% CI=-0.11 to 0.36, p= 0.290), vestibular disorders (SMD= 0.13, 95% CI=-0.17 to 0.42, p= 0.395), or amblyopia (SMD= 0.33, 95% CI=-0.08 to 0.74, p= 0.116).