Board Thread:Versus Debates/@comment-43403813-20200102180859/@comment-9782468-20200123154133

When you factor in that Itachi has such low reserves to begin with, wasting any chakra at all against an opponent formidable enough to warrant usage of the MS is already really risky.

Plus, he already used the MS so rarely that he didn't become close to blind for years. And he knew he was sick and dying; and was basically surviving on drugs when fighting Sasuke. Itachi probably didn't mind eventually losing his sight because his goal was to die to Sasuke anyways.