The sudden flash of light in the eyes is mainly seen in the following two conditions: 1. Posterior detachment of the vitreous body, under normal circumstances, the vitreous body presents a gel state and fits closely with the retina. In certain pathological conditions, such as high myopia or the elderly, the vitreous gel state is destroyed, the liquid component increases and the gel substance decreases, which is clinically referred to as vitreous liquefaction. The liquefied vitreous body does not fit tightly enough with the retina, and when external force hits the eye or when the abdominal pressure increases, the vitreous body undergoes posterior detachment, which will pull the retina and a sudden flashing sensation occurs. When this symptom occurs, it is recommended to go to the hospital for fundus examination to exclude retinal fissure or retinal detachment, especially for those with high myopia, the risk is relatively increased, in most cases, posterior vitreous detachment will not have serious complications. 2. Fundus vasospasm, mostly seen in patients with hypertension or high intraocular pressure, transient spasmodic contraction of the fundus vessels, resulting in a sense of flash in front of the eyes, the symptoms disappear quickly and do not need to be treated.