I've been googling around and came across this thread. It is very interesting.
I can't say exactly what each person might be seeing, but I can share my experience.
I am nearsighted/myopic from age 11. I'm 43 now. More so as I aged. My left eye is now -4.75. My right is -4.25.
At age 27 I noticed floaters in both eyes. A careful exam showed a thinning of the left retina and "scarring", but no threat to my vision.
A sonogram of my eye showed the floaters, which are actually very tiny, but seem larger or smaller depending on their location in the vitreous fluid. (At the back or is it the front of the eye they are projected as larger or vice-versa. I can't remember). They can float off to the side as well and then are less noticeable.
I was told that floaters are common with myopics and nothing to worry about.I'm quite used to them and hardly notice them anymore.
In addition, I first noticed in my field of vision, also around that time, what later was explained by my eye doctor as the white blood cells travelling through capillaries. These capillaries are located somewhere. Maybe the back wall of the eye. I'm not sure. This phenomena too is nothing to worry about I was told, and I don't worry about it. There is even a name--medical term possibly-- for the phenomena, but I can't remember the name.
What I do remember is that white blood cells are larger than the red cells. There are less of them than the red, so under the right conditions, when one goes by, I see it. But not just one-lots.
To this day, against a gray sky, a blue sky, or in the right light against a wall, computer screen etc, I see a whole gang of floaters and also, if I am still and focus a little: the "firefly like" darting white blood cells moving about.
My eyes are fine, but periodic eye exams (every 6 months) were recommended. I haven't stuck to this schedule, but plan to go soon. My grandmother is 94 and blind from macular degeneration for over 10 years. I believe Macular degeneration can run in families. Always good to follow up.
Lastly, I was told that if I ever see bright flashes of light or what looks like a curtain being drawn down in front of my vision or both or other symptoms like, for example, what looks like paint spots, to get to the eye Dr. right away in case there is a retinal detachment. Better to be safe than sorry and I keep the phone number of my eye Dr. with me.
Again, this was only my experience and in no way do I claim to be telling anyone else what their medical condition and/or lack thereof may be.
Maybe they really are seeing the cosmos, and I sure wouldn't want to rain on that parade.