Fiddleford H. McGucket most likely has Strabismus/Lazy eye!
Obviously when he was wearing his glasses all the time, his eyes were righted, but this is just for pointing out the wandering eye over time.
We can see his eyes are starting to unfocus, and he’s not looking through his glasses, which are also broken by this point
Completely unfocused, he’s not worn his glasses in a very long time, clearly.
When he wears only one of the goggle lenses, one eye rights itself completely, while the other doesn’t! His prescription goggles focus his eyes!
And when wearing the goggles, his eyes are completely righted!
As a person with strabismus i would like this headcanon/unstated canon? to be more popular! Representation of characters with Strabismus who are meant to be relatable important characters is like, nonexistent, let’s bring on the headcanon!