Photopsia

Photopsia is the presence of perceived flashes of light. It is most commonly associated with posterior vitreous detachment, migraine with aura, migraine aura without headache, retinal break or detachment, occipital lobe infarction, and sensory deprivation (ophthalmopathic hallucinations). Vitreous shrinkage or liquefaction, which are the most common causes of photopsia, cause a pull in vitreoretinal attachments, irritating the retina and causing it to discharge electrical impulses. These impulses are interpreted by the brain as 'flashes'.

This condition has also been identified as a common initial symptom of Punctate inner choroiditis (PIC), a rare retinal autoimmune disease believed to be caused by the immune system mistakenly attacking and destroying the retina. During pregnancy, new-onset photopsia is concerning for severe preeclampsia.

Photopsia can present as retinal detachment when examined by an optometrist or ophthalmologist. However, it can also be a sign of Uveal melanoma. This condition is extremely rare (5–7 per 1 million people will be affected, typically fair-skinned, blue-eyed northern Europeans). Photopsia should be investigated immediately.

...
Wikipedia