Update: after seven days' treatment with metronidazole and frusol daily, there's no improvement. Eye is still cloudy, frog still swollen up, still swimming in circles (maybe a little less). There's still three more days of frusol treatment to go, but my hope for a recovery is fading. The one mercy is that toad's condition has not worsened significantly, but I wonder whether all that stress has been for naught. I will return to the vet soon but I doubt much good news will come of it. I suppose we can now rule out certain bacteria and protozoa as culprits, since they should have been cleared out by the metronidazole, but other infections might be to blame.