Sudden blindness of the left eye, and then a moment later, may be a transient spasm of blood vessels, cardiovascular and cerebrovascular diseases, or the fundus of the blood circulation embolism and other factors. 1. Transient vasospasm: this phenomenon is more common in the elderly who suffer from high blood pressure and high blood fat. The patient will experience a transient blindness that lasts for a few seconds or minutes and then returns to normal. 2. Cardiovascular and cerebrovascular diseases: it may be triggered by cardiovascular, cerebral and cerebrovascular tumors, and the transient blindness may be caused by the tumor pressing the optic nerve of the brain center. 3. Fundus blood circulation embolism: it may also be caused by brain diseases leading to fundus blood circulation embolism, such as retinal detachment, retrobulbar optic neuritis and retinopathy. After the attack, the proliferating blood vessels may rupture and bleed, resulting in accumulation of blood in the vitreous cavity, which may cause sudden blindness or a sharp decrease in vision. There are many reasons for sudden blindness in the left eye, so patients should go to the hospital for examination and treatment of the cause.