how come obito didn't go blind from MS

[Monoblock]

yeah you're right I went back to check, but i guess hashirama's cells did help. Why didn't he just give them to sasuke

Give what to Sasuke? Both of his eyes? If that's what you asking then Sasuke's eye got sliced and he only needed one.

 

[Dwolf]

Only his body not his eye. Zetsu and Hashirama cells were used to heal him.

 

[Monoblock]

Its kind of unclear but even if it was crushed it's been confirmed that Zetsu and Hashirama's cells saved his eye and body. Madara also gave him his eye. Its been half-implied that his Mangekyo was awakened for a brief moment and allowed him to slip through the rocks (Madara said something similar to that when Obito awoke for the first time)

 

[acri1]

Senju DNA

Spoiler