I don't see why everyone seems to think that Izanami HAS TO be used in Itachi's right eye. Where does it ever say in the Manga that Izanami uses the right eye and Izanagi uses the left eye? It doesn't. Just because Tobi used Izanagi with his left eye doesn't mean that Izanagi ALWAYS has to be used with left eyes, and that Izanami, since it is its partner/equal, uses the right eye.
If anyone actually reads the damn Manga you would remember that Danzo thought about using Izanagi against Sasuke with Shisui's eye after Danzo ran out of all the eyes on his arm. And guess what, that was his RIGHT eye. So it doesn't matter which damn eye it is.
Anyway, I agree with the OP. Itachi already got hit before by the cave spikes, and his eye was gone, just because it is gone again this time doesn't mean anything. And to the person who said that oh he is already regenerating and his left eye is there but not his right...how do you know he regenerated already? It doesn't look any different, how can you tell that he regenerated completely? You can't.