The youngest Stark sister lost her eyesight at the close of Season 5, as punishment for stealing a face from The House of Black and White to go on a killing spree. But Arya Stark gets her eyesight back on Game of Thrones in Season 6's third episode "Oathbreaker" as an apparent reward for mastering blind sparring and maintaining her anonymous identity to Jaqen H’ghar.
Poor Arya had been getting the crap beaten out of her day in and day out by a staff-wielding Waif who is evidently trying to teach The Girl how to fight again without her eyesight. Except instead of patiently and kindly teaching her (because lol this is Westeros), The Waif basically just springs on Arya out of nowhere, lands a bunch of blows, and leaves Arya to her instincts to fend off attacks. Arya does eventually get better at it (after who knows how many split lips) and, after holding her own in a spar, Jaqen approaches her.
Arya has also been successfully disassociating herself from her past life in an effort to become an anonymous Faceless assassin. She is able, in a scene spliced between her sparring and her questioning, to recall Arya's life, while identifying herself only as "Girl." Eventually, Jaqan offers her the same bribe from earlier in Season 6 — she may have her sight returned if she admits her name is Arya. But she repeats, faithfully, "A Girl has no name."
"If a Girl is truly no one, she has nothing to fear," he says before handing her a bowl to drink from. She takes a sip, blinks a few times, and, faster than you can say Valar Morghulis, Arya's eyes are clear again.
"Who are you?" Jaqan asks her one more time.
"No one," she repeats.
While it's heartbreaking to watch Arya claw her way back from blind beggardom, her years on the lam have taught her nothing if not adaptability. We can assume that Arya is simply doing what is necessary to reunite with her family, but that might be wishful thinking at this point. It's entirely possible that, upon finishing off the rest of her kill list, Arya will have been brainwashed to the point of actually not being able to connect with her family any longer. And if she is still Arya somewhere deep inside, The Girl is certainly doing a convincing job of faking it.