I have double vision when using only one eye, things look just slightly off, like a ghost image on an old tv, or when you get really up close to an old glass-silverbacked mirror. Happens in my left eye only.

After way too many visits to ophthalmologists and a neuroophthalmologist, someone finally found my left eye has keratoconus. This means the cornea has uneven thickness in places. Which gives you the effect as if looking through an old piece of glass that has a ripple or two in it. Hence the strange, unclear, sort of double vision effect.

Nothing dramatic to worry about. Not much to be done about it, either. Which would not be such a big deal, except my right eye has some much bigger problems going on, the left eye works okay but has this little problem that keeps things from being quite clear.