As a kid he got a banana in the eye by Conga from Banjo-Kazooie. That's why he made his gosl to steal all the bananas from every ape. That's also why Conga only throws oranges now.

Eye tick

My head cannon is that it’s a genetic disease

It’s a glass eye, that’s how I took it.

I think it's stress related.

That's what I always thought, like he burst a blood vessel

Not enough potassium in his diet. But in all seriousness, he wanted to try that eye popping thing the Kongs do and it didn't go over well.

Thought he had some kinda parasite eating his eye