This condition can be caused by many diseases: 1) a transient black haze, which usually lasts for a few seconds or minutes and can be caused by retinal artery spasm or postural hypotension, which can quickly return to normal and therefore usually does not require treatment; 2) vitreous hemorrhage, such as trauma to the eye or retinal vein obstruction, which causes blood to accumulate in the vitreous cavity and can lead to sudden loss of vision; 3) retinal artery obstruction, which is also a common ophthalmology emergency and can cause painless loss of vision. This is also a common emergency in ophthalmology, the symptoms are painless loss of vision, for this case must be taken seriously, early detection and early treatment, if you miss the best treatment period, such as the condition of more than 6 hours, vision recovery will become very difficult; 4, see the optic nerve disease, such as optic neuritis, will also The eyes suddenly appear to be unable to see clearly or invisible.