There are several causes of flashes. The most common cause is a posterior vitreous detachment (PVD), but a retinal tear, migraine and inflammation can also cause the same visual symptoms.
In other articles, a PVD and retinal tear have been well covered.
Flashes Due to Migraine
Without getting too specific, there are visual migraines that yield a scintillating light pattern, often confused with flashes. The array of lights las (Read more...)