Purpose : This study aims to measure, in real time, the temperature, humidity, and heat index within HMD-based VR devices during dynamic physical activity and to examine how these microenvironmental changes affect dry-eye symptoms and visual discomfort. The results will provide an empirical foundation for enhancing user safety and designing optimized VR environments through effective thermal and humidity management. Methods : Twenty-eight physical education students participated, performing an interactive VR boxing program using Oculus Quest II. HMD internal temperature, humidity and heat index were continuously monitored every 2.5 seconds using an Arduino–DHT11 system. The experiment included 15 minutes each of resting, exercise and recovery phases with heart rate maintained at 30~50% HRR. Dry eye assessments were conducted pre- and post-experiment using non-invasive tear break-up time (NI BUT), Schirmer test, and Ocular Surface Disease Index (OSDI) questionnaire. Paired t-tests and chi-square tests were applied (p<0.050). Results : Participants (mean age 23.44±1.17 years) showed no significant changes in NI BUT and Schirmer tests (p>0.050), whereas OSDI scores increased significantly (10.49±2.52 → 18.28±4.01, p<0.050), indicating elevated subjective ocular discomfort. HMD temperature, humidity and heat index rose most sharply during the initial exercise phase (15~18 min, p<0.001), followed by gradual stabilization. Short-term high-intensity VR use induced abrupt internal rapid changes, associated with increased subjective visual fatigue. Conclusion : Intense physical activity in VR rapidly elevates HMD temperature, humidity, and heat index, exacerbating thermal discomfort and visual fatigue. These effects are reversible post-activity, emphasizing the need for rest, ventilation strategies, and HMD design considerations to ensure safe and comfortable active VR use.