The flash in myopic eyes is due to the occurrence of posterior vitreous detachment. Posterior vitreous detachment refers to a separation of the intravitreal cortex from the inner surface of the retina. Normally, after birth, the vitreous body is a viscous jelly-like substance that is tightly bonded to the retina. As the vitreous grows older, the viscous material in the vitreous gradually liquefies, and on top of that, the vitreous gradually separates from the retina. When the vitreous is about to separate from the retina, the retina is pulled, and the pulling causes electrical activity in the retina, resulting in a flash in front of the eyes, which is caused by the pulling of the posterior vitreous detachment. Since the retina of myopic eyes is relatively fragile, it is necessary to refrain from strenuous activities after the flash occurs to prevent the force of posterior vitreous detachment from being greater and causing retinal fissures.