Sarada is a troll, She doesn't need glasses

[Guitar Hero]

Righto.

 

[rollin]

she only started wearing the glasses after she got sick

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[baul 24]

Nah most legit explanation is kishi want to troll us by making us think she is karin's daughter so the glasses and keep up the drama, other than that i don't find any other reason since he introduced her with glasses need to keep her that way through the entire manga nothing else.