There are black lines flying in front of the eyes, most of the patients due to posterior vitreous detachment leading to the appearance of weiss ring or vitreous clouding material, and a few patients due to hemorrhage caused by retinal lacunae, retinal vascular diseases, retinal detachment, and so on. After vitreous liquefaction due to old age, long eye axis of high myopia, etc., the posterior border membrane of vitreous is easy to detach from the retina, and in the process of detachment or after complete detachment, black shadows fluttering in front of the eyes are easy to appear. Among them, most of the thread-like black shadows are weiss rings after detachment, because the adhesion between the vitreous body and the edge of the optic disk is very tight, so the rings will appear after detachment. In a few patients, because of the close adhesion between the posterior border membrane of the vitreous and the retina, it is easy to pull the retina in the process of detachment, resulting in cracks, detachment, etc., or a small amount of hemorrhage occurs due to retinal vascular disease, which is also manifested as a black shadow fluttering in front of the eyes. Therefore, it is recommended that patients should consult a doctor to check the fundus in a timely manner after noticing the black lines fluttering in front of their eyes.