I’m talking about Eckleburg, you’re talking about his sign.
And therefore, according to Fitzgerald, you do not know that Eckleburg was a "failed oculist." That's not in the text. The oculist's fate is left undeclared for certain.
See, it helps to follow the text, whether it is written by Fitzgerald or God.
If you want to allegorize the good doctor, as many do, then he's definitely not "failed."