The appearance of black lines floating in the eyes when looking at something is usually a sign of fundus disease, including vitreous disease, retinal disease or optic nerve disease. Therefore, when this symptom occurs, it is recommended to first go to the hospital for a detailed fundus examination, and only when the specific condition is clarified can active treatment be carried out. If it is a vitreous clouding, then it is important to decide how to treat it depending on whether it is a physiological vitreous clouding or a pathological vitreous clouding. Physiological vitreous clouding, also known as mosquitoes, is a condition that does not require treatment because it only manifests as mosquitoes in front of the eyes, but does not cause vision loss. Pathological vitreous clouding is usually due to various causes of fundus hemorrhage, so the accumulation of blood in the vitreous cavity requires symptomatic treatment according to the specific cause. In the case of retinal fissures, retinal detachment and these diseases, then aggressive surgical treatment or retinal laser photocoagulation is required.