I don't understand this sentence structure

Hola Doug R. and Clara M.

That’s a great question and your intuition is right that “I can’t believe my eyes” works perfectly in English. Spanish, however, often expresses this idea a bit differently.

In “No puedo creer lo que ven mis ojos”, the verb ver is necessary because “lo que” introduces a relative clause that means “what my eyes are seeing.”

So the structure is:

No puedo creer + lo que + verb + subject

Literally:

I can’t believe what my eyes see / are seeing.

If we said “No puedo creer mis ojos”, it would sound incomplete or unnatural in Spanish, because creer normally needs a clause or idea to believe, not just a body part on its own.

So while English uses a fixed idiom (my eyes), Spanish prefers to make the idea explicit by saying what the eyes are seeing.

Both languages express the same meaning but they just package it differently.

Hope that helps clarify it!

Saludos

Silvia