Flashes in the outer corner of the eye may be the result of a detached retina, vitreous detachment or an ocular migraine. These conditions are usually considered medical emergencies.
The sudden appearance of flashes in the corner of the eye may be a sign of the vitreous pulling away from the retina. In some cases, the retina itself may detach from the back of the eye. When retina detachment occurs, an eye surgeon has to take immediate action to reattach it before vision becomes permanently impaired. According to WebMD, flashing lights in one eye that are accompanied by headaches and blind spots in the field of vision are symptoms of ocular migraine.