I personally think it's closed on purpose, hopefully when he gets an extreme diff he'll show what exactly is happening with that eye.
Ironically in Rurnoi Kenshin there is a technique called Shin no ippo, when the move is used the opponent with a weaker will cannot move, you become paralyzed from the chi that's being released.
Here's an explanation from the Wiki :
He projects his chi through his eyes at his opponent. This completely hypnotizes the target and Jin-e usually uses it to paralyze his target, leaving them unable to move. He can control how strong the effects are and can also use it on himself to make himself believe he is invincible and greatly increase his power. He can also use it to paralyze a person to the point of paralyzing their lungs, making them unable to breathe, causing them to suffocate and die. There are three methods to break the effects of the spell: It can be dispelled by himself, his opponent's chi must have a similar strength to his own in order for them to break it, or he must be killed.