Posterior Vitreous Detachment (PVD) can cause blood leakage into the eye, analogous to the far more serious retinal detachment. Its age related mostly, but a bloody good bang can bring it forward. Aside from giant floaters, you get a cloud of blood corpuscles which resolve (at least in my case) as floating circles. I was beseiged by ASCII "0" characters, as each eyeball went.
A different kind of TV interference but it also reminded me of B&W TV in 625 line days, with a weak signal.
In my case it lasted about a month. Either your brain-eye ML works out how to ignore it, or the blood subsides, or a bit of both.
Sucks to be old, but considering the alternatives I'll take it.
