The sudden appearance of blurred vision, shadows or light spots in the visual field are usually caused by the following reasons: a. Due to bleeding in the fundus, which is common in patients with underlying diseases such as diabetes or hypertension, and can be diagnosed through detailed fundus examination and ultrasound examination of the eyes. Second, due to hypotension or hypoglycemia, the above diseases can lead to temporary retinal blood supply deficiency or inadequate energy supply, resulting in visual abnormalities, manifesting as dazzling, and the symptoms will soon disappear as blood pressure and blood sugar return to normal. Third, triggered by the visual aura of migraine, visual abnormalities caused by abnormal discharge of the visual center, usually about half an hour after the appearance of dazzling symptoms, there is an obvious headache occurs.