In vitrectomy, if the vitreous cavity is injected with gas, you need to sleep on your stomach for about a week after surgery, if the vitreous cavity is injected with silicone oil, you need to sleep on your stomach for about a month, if the vitreous cavity is neither injected with gas nor silicone oil, you do not need to sleep on your stomach. If there is no retinal detachment but only proliferative membrane on the retina, it is necessary to inject gas into the vitreous cavity after detaching the proliferative membrane to prevent retinal detachment, and the injected gas can be absorbed by itself in a week or so. If there is retinal detachment, silicone oil should be injected. The reason for sleeping on the stomach is that the gas and silicone oil float on the retina when lying on the stomach, which can play a fixed role.