Up until recently, I had never heard of scintillating scotoma, but my boyfriend is an occasional sufferer - and although that is not so fun for him, it's certainly a handy suggestion for an Interesting Medical Fact of the Week!
The word scintillating comes from the Latin scintillare - to sparkle, glitter, gleam or flash. The word scotoma comes from the Greek for darkness. So at first etymological glance, it would appear that a scintillating scotoma is something of an oxymoron.
Medically speaking, a scintillating scotoma is a symptom which often precedes the onset of migraine, although it can also appear as an isolated symptom without headache. Wikipedia describes it as follows:
Scintillating scotoma usually begins as a spot of flickering light near or in the center of the visual fields, which prevents vision within the scotoma. The scotoma area flickers, but is not dark. The scotoma then expands into one or more shimmering arcs of white or colored flashing lights. An arc of light may gradually enlarge, become more obvious, and may take the form of a definite zigzag pattern, sometimes called a fortification spectrum, because of its resemblance to the fortifications of a castle or fort seen from above.
The visual anomaly results from abnormal functioning of portions of the occipital cortex, at the back of the brain, not in the eyes. Symptoms typically appear gradually over 5 to 20 minutes and generally last fewer than 60 minutes, leading to the headache in classic migraine with aura, or resolving without consequence in acephalgic migraine.
Sounds kind of pretty, right? Unfortunately, even if you don't get a headache or other symptoms, it does massively mess with your vision until it resolves. If you search online, you can see a selection of artist's impressions of what scintillating scotoma can look like to sufferers: