Photopsia is the presence of perceived flashes of light in the field of vision.
It is most commonly associated with:
posterior vitreous detachment
migraine aura (ocular migraine / retinal migraine)
migraine aura without headache
scintillating scotoma
retinal break or detachment
occipital lobe infarction (similar to occipital stroke)
sensory deprivation (ophthalmopathic hallucinations)
age-related macular degeneration
vertebrobasilar insufficiency
optic neuritis
visual snow