This is a thing, it’s bizarre as heck but there are real cases where one personality has a significantly different ocular readings to another. There’s a few different possibilities why this happens, one of which is that one personality has memories of trauma that the other does not have, and this leads to a deterioration in vision from the mental state.

I say this because the latest incarnation of Kaneki is wearing glasses during battle, something that he has never done before. Also during his time as Haise, whenever he is trying to remember something Kaneki related he would get headaches/sensation of pain in his eyes, which I believe are from Arima stabbing him in V14.

When Haise was thinking of using masks to infiltrate ghoul society to get info he feels that his eyesight got worse. This was after he got the eyepatch mask and a signed copy of Takatsuki Sen’s novel that told him how to spell Keneki’s name. It could be that as he uncovers more of Kaneki, his eyesight reflects that by getting worse.

His wearing glasses now may not just be Kaneki copying Arima, he may really need them all the time. Thanks papa Arima.

Here are some abstracts of the research done into eyesight and multiple personalities.

Visual function in multiple personality disorder.



Optical differences in cases of multiple personality disorder.



Optical differences in multiple personality disorder. A second look.