I've had migraines where I saw flashes and also one or two where my eyes were so sensitive to light that I couldn't see...but never had items MISSING from my vision. That's a little spooky.
The flashes are how you can tell you're having a migraine and not a stroke. In strokes, you abruptly loose your vision and it doesn't come back.
In mini-strokes, you abruptly loose your vision and it comes back a day or so later.
In migraines, you slowly loose your vision and then it starts to flash and show zigzag lines, then you get your vision back. I was having a hard time focusing my eyes in the very first place this morning (not unusual, I have very dry eyes) and had actually put some eye drops in, hoping that would help. Then I gradually noticed the vision loss. And it's not like anything goes dark...it is just like it's not there anymore. That's when I started to panic, but then I saw the shimmering. It looks just like shimmering sparkling water rippling. Then I knew what was happenening and relaxed.
It actually started shimmering in the middle of me telling Steve and I actually went "Oh! It's ok! It's a migraine!"
Anyway, it's the gradual onset that differentiates it from more catastrophic events.