In the sunlight, the eyes see a lot of black shadows flashing, which is usually a manifestation of vitreous clouding and posterior vitreous detachment. 1. Vitreous clouding: If there is a flying mosquito in front of the eyes, it is normal for most middle-aged and old people and can be left untreated; this phenomenon can also happen to young people, especially those who are highly nearsighted or have trauma. 2. Posterior vitreous detachment: If there is a sudden flash of light in front of the eyes, it indicates that there is vitreoretinal traction. It is recommended to go to the ophthalmology department for a detailed examination of the fundus to see if there is any abnormality such as retinal tear or retinal detachment. If there is a fixed shadow in front of the eyes, or even a halo of flashes, retinal detachment is very likely. There are other reasons for seeing a large black shadow flashing in the eyes under the sun, and you need to go to the hospital as soon as possible to get a clear diagnosis and active treatment, so as not to delay the condition.