This question already has an answer here:
A student asked me tonight why we say "something caught my eye," and not "something caught my eyes." This is not just limited to eyes but also:
"lend me your ear." "Can I give you a hand?" or "an eye for detail."
Is this because we are not thinking of the actual body part but it's function?
This question was asked before but the answer and comments do not address the question very well. Why does “something catch my eye” but not “both my eyes”?