Nazgûl-related blindness?

[MLD-Grounds-Keeper-Willie]

i agree with a lot of the things said already. But,

...Did you ever think of the time when he was struck by the morgul blade?-Gandalf himself said he would carry the unhealing wound all his life...-well maybe this has some connection to your question

That might make the most sense if it was the same ringwraith in the Emyn Muil as it was the same that stabbed Frodo with the morgul blade. That wound seemed to cause Frodo great pain when he came back by Weathertop, and that was pretty long after he had been stabbed. So, if it was the same ringwraith, it would only make sense if just having him near Frodo caused him pain. Not only that, but as many others have said, if you consider all the other factors, especially the ring, having Frodo going temporarily blind does't seem that far-fetched.