The phenomenon of double vision in the left eye may be due to physiological reasons (e.g. overuse of eyes, etc.) or pathological reasons (e.g. refractive error, cataract, etc.). 1. Physiological reasons: overuse of eyes, staying up late, facing electronic products for a long time can lead to visual fatigue, which may appear in the left eye to see things with double images, blurred vision and other symptoms. 2. Pathologic causes: (1) Refractive error: the most common refractive error is myopia, and it occurs in adolescents, due to the parallel rays of light can not be focused on the retina of the left eye, and thus there may be symptoms such as seeing things with heavy shadows, loss of vision and so on. (2) Cataract: Cataract is a visual disorder caused by clouding of the lens, which may also cause double vision in the left eye, accompanied by vision loss and glare. If the above symptoms occur and physiological causes are ruled out, it is recommended to go to the hospital to find out the cause of the disease and actively cooperate with the doctor for treatment.