Quote Originally Posted by Kensee
Then what does it do? Gives you a huge hang over? Anyone else can comfirm the "doesn't give you blindness due to usage?"
The scene that brought the whole blindness to question was a very debateable series of dialogue between Kakashi and Itachi that came down to one of two probable scenarios:

1) Kakashi was eluding to Itachi losing his vision
2) Kakashi was eluding to having a secret weapon that Itachi neglected to notice

Many people sided with the 1st theory, as the likelyhood of kakashi suddenly having a jutsu that would elicit such fear in Itachi seemed unreasonable within the bounds of the Naruto realm. However, when he later unconvers his mangekyou sharingan, it is confirmed that this is, in fact, the case.

As a result, the consensus for the most part silently shook off the notion of itachi going blind.