Generally speaking, the floating black shadow in front of the eye is mainly caused by the cloudy substance in the vitreous cavity of the eye. The cloudy substance in the vitreous cavity forms a black dot in front of the eye because it blocks a small part of the vision. The vitreous body is inertial movement with the eye movement, so when the eye movement, the vitreous body also occurs movement, the vitreous cavity of the cloudy material caused by the black dots in front of the eye will also occur movement, thus forming a black shadow in front of the eye has been floating, like a mosquito flying in front of the feeling. Then, the vitreous cavity and how the formation of cloudy material? There are 70% of the vitreous cavity cloudy material is due to physiological factors, mainly because with the increase in age, intraocular metabolic changes, vitreous liquefaction collapse and vitreous detachment of the formation of vitreous cavity cloudy material, resulting in a black shadow floating in front of the eyes, medically called “physiological flying mosquitoes”, although the mosquitoes fly in front of the eyes very Nasty, but no impact on vision. In addition, there are 30% of the black shadow floating in front of the eyes, is caused by disease, mainly intraocular hemorrhage, inflammation and other diseases caused by. The main and most serious diseases are retinal fissure formation and retinal detachment occurring. The black fluttering shadows and flashing lights in front of the eyes indicate the pulling of the retina by the vitreous body, during which the retinal fissure is likely to be formed. The high prevalence of black shadows in front of the eyes is mainly in middle-aged and elderly people, highly myopic eyes and diabetic people. If these people suddenly develop black fluttering shadows in front of their eyes, they should seek prompt medical attention and have your fundus examined by an ophthalmologist, including a dilated pupil and an ophthalmic ultrasound. If the doctor diagnosed you as “physiological mosquito flying”, then you should not panic, if the doctor diagnosed you as retinal fissure formation, then you have to rush to laser treatment, so as not to develop into retinal detachment and lead to blindness.