Question

If it's different, when i have to use "in my eyes" or "on my eyes"

Answer 1

In my eyes = there is something (physically) in my eyes ' I have sand in my eyes' however I can't think of a situation where I would use 'on' my eyes - perhaps using face cream on my eyelids (not on my eyes).

' In my eyes' sounds like a poor translation of ' à mon avis', as I see it, in my opinion. 

Hope this helps

Answer 2

In my eyes, you can use this expression to make notice that there's literally something bothering your eyes like: I have cream in my eyes.

Also you can use that expression as a figurative speech, for example:  I can't change that idea, they're innocent in my eyes. for you they look innocent, be it like that or not.