Yesterday, shortly after arriving at work, I noticed a rather large, gray "floater" in my field of vision. I've had floaters as long as I can remember, but this one was different. It was much larger (about the size of a fingernail at arm's length) and when I closed that eye, it would turn white—with circulating black flecks inside it. This was not normal, and of course internet searches convinced me I was dying.
My dad had a history of detached retinas, so I feared the worst and called my opthamologist. I saw her yesterday afternoon. As I described to her, it was like the afterimage you get when staring into a bright light…except it never fades away.
She dilated my eyes and looked around in them for several minutes. Turns out it is a fairly common aspect of aging; the vitreous gel (the substance "inflating" the eyeball) starts to break down as we get older, and in doing so it can pull away from the retina, causing these spots. There was no sign of tearing or separation or macular degeneration, so there's that, but it's annoying as hell because it's dead-center in the field of vision in my left eye (my dominant, "reading" eye) and because I'm so aware of it now I'm getting eye-strain headaches. "The spot may disappear completely as it migrates, or it may stay put." How reassuring.
She noted to call immediately if anything changes—especially seeing bright flashes, but otherwise it's nothing to worry about. I made an appointment to see in her in month's time to followup.
Good luck with this.
Getting older is much less fun than I expected.