Discussion
angulation, head or neck flexion, HT, neck/shoulder pain
The main results of this randomized crossover study were that using prismatic loupes (compared to traditional loupes) reduced two ergonomic risk factors – head inclination and neck muscle activity –without increasing surgical errors. However, in two of three tasks, the completion time was prolonged when using HT loupes.To our best knowledge, this is currently the largest performed study that focuses on the effects of prismatic loupes use among surgeons. There was a significant reduction in head inclination when using the two prismatic loupes compared to traditional loupes. This is an important finding since the forward head inclination likely is a primary contributor to the high frequency of neck/shoulder pain among surgeons. An angulation of 15° in the prism of the LT loupes resulted in a 13°–14° reduction in the group median of the 50th percentile head inclination, while a 48° angulation in the prism of the HT loupes reduced the head inclination by 22°–26°. While factors such as eye rolling and frame angle also influence the impact of loupes on head inclination, the results consistently show a trend: increased angulation in the prism of the surgical loupes correlates with greater head inclination.A few studies have reported that the usage of prismatic glasses can reduce head or neck flexion among dental workers, with an angulation angle of 5° in the prism leading to a reduction of 6.5° in the 50th percentile head inclination (This study also found that in comparison to that with the use of nonprismatic loupes, the neck muscle activity significantly decreased on both sides when using prismatic loupes, with a 0–23% reduction in the group median of the 50th percentile muscle activity for the LT loupes and a 32–42% reduction for the HT loupes. This reduction was smaller than in a previous study (~40% reduction in the group mean of the 10th percentile), which used loupes with a 90-degree angulation for a simulated dental task (Regarding surgical performance, no significant difference in surgical errors was found between the nonprismatic loupes and the LT and HT prismatic loupes. However, it took the participants longer to complete the activities in two of the three simulated tasks with the HT loupes than with the nonprismatic loupes and LT loupes, though the practice session provided for all participants before the trials were short. Another finding was that the upper arms were slightly more static when the surgeons used the HT loupes than the others. In the previous study by Smith et al. (Reduced physical workload is related to reduced risks of developing MSDs (It is important to note that factors other than angulation in the prism should also be considered when choosing or designing prismatic loupes. The higher angulation can lead to significantly lower head forward inclination angles, but the user experience of such loupes might, on the other hand, be worse than those with slightly lower angulation. This is revealed by the results that LT loupes were preferred by most surgeons in this study, while HT loupes were less preferred. The comfort, e.g., “lightweight and fit,” visual quality, and the presence of glasses around the loupe for side vision during surgery were important factors contributing to the surgeons’ preference for LT prismatic loupes in addition to the resultant neck posture. For the future design of prismatic surgical loupes, finding the most suitable angulation for different types of surgeries is worth further studying.