A flash of light in the eye is mostly caused by vitreous shock. The vitreous body is a stable jelly-like liquid when a person is young, and is relatively tightly connected to the retina at the fundus of the eye. However, with age or myopia, the jelly-like substance is not strong, and it gradually concentrates and gradually separates from the retina, and the process of separation from the retina will pull the retina and cause retinal shock, and each pull on the retina may cause a flashing sensation. With the movement of the head or eye, intravitreal shock will be generated, and the shock aggravates the pull on the retina, so often when the eye moves or does strenuous exercise, causing the presence of intraocular flash sensation. If you have a flashing sensation in your eyes, go to the hospital for a dilated eye exam and check the peripheral fundus for any fissures or degeneration for timely treatment.