A frequent flashing sensation at the edge of the eye is caused by the vitreous pulling against the retina during posterior detachment, which is a very dangerous sign. When this flashing sensation occurs, you should promptly visit a regular eye care provider and undergo appropriate careful examination to determine if fundus pathology is present. If retinal fissures are present, appropriate laser treatment is required to avoid serious complications such as retinal detachment. If there is no fundus lesion, close observation is also needed, while avoiding eye collisions, excessive eye fatigue and vigorous eye rubbing. If the flashing sensation is aggravated, or if it is accompanied by loss of vision and black shadows floating in front of the eyes, prompt consultation with the ophthalmologist is needed to avoid delaying the condition.