The only one I could think of.
'He didn't learn how. That's why he couldn't,' I said.
I don't think there's a subject related to eyesight-fixing in Hogwarts. Remember when Malfoy blew up Hermoine's front teeth? She went to the hospital wing to get them fixed. And she was the genius of her batch, who happened to know so much.
Knowing more than Harry does, one would think that she could have gotten them fixed herself. But she couldn't. Because she wasn't taught how. If everyone who attends Hogwarts should be able to do everything - like what is expected of Harry - there shouldn't be a need for the hospital wing in the school, right?
Harry was interested in becoming an Auror. I bet they don't teach these Aurors-in-training how to fix their eyesight; like how the people who joined Police Force aren't taught how to diagnose and cure fever. It's not part of the course. Hehe.
And some days ago I googled the question. One of them Pottheads answered like I did. With less explanation, of course. But I get what she meant.
'Sama macam kitalah, ambik TESL takkanlah boleh reti buat brain transplant pulak tiba-tiba kan?' I added.
* * *
I thought the answer was obvious.
Well, what do you think?