<p>Previous studies have demonstrated that lifestyle was associated with myopia. This study used Mendelian randomization (MR) analysis to examine the causal relationships between the time of computer use, the time outdoors in summer and the time outdoors in winter and myopia. Subsequently, univariate MR (UVMR) analyses were carried out respectively on the three exposure factors and myopia, and the results were mainly based on the inverse-variance-weighted method. In addition, sensitivity analyses were also conducted, including heterogeneity tests, horizontal pleiotropy and leave-one-out methods, to evaluate the stability of the MR results. Multivariate MR (MVMR) analysis was also carried out. The UVMR analysis showed that two of the exposure factors had causal relationships with myopia: the time of computer use was a risk factor, and the time spent outdoors in summer was a protective factor. However, the time spent outdoors in winter had no direct impact on myopia. Furthermore, further mediation analysis showed that the frequency of solarium/sunlamp use was a mediating factor between the time outdoors in winter-myopia, and the mediating effect accounted for 36.93%. In conclusion, when multiple factors occurred simultaneously, the time of computer use in summer and the time of outdoor activities had a potential impact on myopia, and the time outdoors in winter affected myopia through the frequency of solarium/sunlamp use.</p>