I have been meaning to share these facinating phenomena:
Feel free to comment or share more of them.
My favourite two from medschool are
- being able to see the white blood cells crawl through the retinas capillaries when you look at the blue sky for long enough and
- Purkinje Figures.
Especially experiencing the latter was stunning.
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Has anyone ever experienced a phenomenon, where you get a small curved blob near the center of your vision that gradually grows toward the edges? It’s hard to see through it (strong blur), and I think it even flickers rainbow colors a bit. The strange thing is that I can see it with both eyes AND each eye individually. I have not found any formal description of it yet, any chance it’s something you know?
Add to that negative and positive photopsia (which I’ve experienced since cataract lens replacement surgeries) and scintillating scotoma (migraine aura) (which I’ve occasionally experienced for about 18 months now). This simulation of the latter is probably the closest to my personal experience. Fortunately there’s never been any associated pain. Let’s hope it stays that way. I had doc exams, etc. and there are no problems with my eyes related to the auras, so it’s neurological most likely. And apparently it’s not all that uncommon.
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Lol that actually may be what I experience on and off for the past 13 years or something. Thanks Len, you’ve solved my decade old mystery of being unable to describe the thing 
Sometime I got two of those one after another, and then I could have none for 4-5 months. It’s bizzare, because I don’t think I experience migraines
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The first time it happened, I was almost a bit freaked out but now I’m accustomed to it. It’s fairly rare, though. The simulation is more of a perfect crescent, more perfectly defined than mine. But the angular dark lines and scintillating colors match very closely. I’ve not experienced any music with mine, though. 
It starts small in the center of my vision then slowly expands until it exits my FOV, usually taking about 15 to 20 minutes. When it first starts it can make reading or other visually-detailed tasks momentarily more difficult, but otherwise doesn’t really impact me. I’ve even had it happen while freeway driving and it was no problem ignoring it.
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Yeah, that’s pretty much my experience too.
That depend on whether it goes left or right. If it expands to the left, reading is still somewhat fine, but difficult if it expands to the right, since your brain likely pre-reads words ahead or something.
Someone said it’s like drugs but without the joy 
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One I learned about early in my life (younger than 10) is Haidinger’s Brush. You can find it in a clear sky 90 degrees from the Sun. I found it as a child and wondered what it was, and even if it was real. I searched and found the terminology somewhat later.
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Thank you for the links, especially the simulation. This i am experiencing too sometimes, mostly when i forgot to drink enough of water.
Never was worried about it, because its always gone after a few minutes.
More interest and participation than I expected! 
I suffer from all types of headaches including migraines but no auras.
I see some kind of visual noise, especially on low light or dark colors in averagely lit rooms, it’s like very fine color film grain (but obviously faster), most of the times I don’t notice it at all. I one asked an ophthalmologist about it but she dismissed it without explanation and to this day I don’t know if this is normal, as in, a limit of human vision just like a camera, or if it’s a type of visual snow.
It doesn’t bother me at all and has had no change for years so I am not too worried. Especially since I don’t notice it when outdoors or in bright scenes.
There are additional phenomena that I (and others) may have previously shared such as impossible colours and special/new colours that occur under certain circumstances. Feel free to search and read about them if you have not already done so. 
We are not even getting into how other creatures see things differently from or strangely similarly to humans! 