Visits doctor for operation - what could go wrong? (5,2)
I believe the answer is:
drops in
'visits' is the definition.
(dropping in is a kind of visiting)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for drops in that I've seen before include "Comes to see" , "Calls casually" , "eye thus getting less inflamed?" , "Casually visits" .)