photopsia; the brief perception of light that is purely subjective and accompanies a pathological condition, especially of the retina or brain
(Photopsia) Traction on the retina experienced visually as brief flashes of light--lightening streaks. Sometimes more noticeable with head movements. Sometimes a warning symptom of impending retinal tear or detachment.
Any flashes in vision should be investigated by an eye doctor. Most are due to a tugging on the retina by the vitreous gel and are relatively harmless. However, a detached retina may also produce flashes and this is an emergency.