That was never said.Infact after Sasuke fought bee he was showing eye problems.
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And after some rest he was back in full condition.This time he used his eye more,so he should worse effects but perhaps after some rest he would have recovered.It was never said he would of been blind without Itachi's eyes at that pointand besides if it was Full conditon MS Sasuke Vs Full condition SM Naruto we could say Sasuke would win simply based on the fact that Naruto admitted he would NEED the Kyuubi's chakra to FIGHT Sasuke.