You compare Miyata to Aoki and Kimura? Bad comparasion.

Takamura is supposed to be the larger than life character, the invinsible giant, god on earth etc. etc. It will break the illusion if he got the eye condition. Besides this manga isn't really that realistic, i mean they are punched bloody in every single fight and no one ever gets any really serious injuries exept that southpaw guy who fought Sendou and he was a minor character. I don't think any of the mains will get carrier threatening injuries.