Swelling troubling your eyelid, primarily (4)
I believe the answer is:
stye
'swelling' is the definition.
(stye is a kind of swelling)
'troubling your eyelid primarily' is the wordplay.
'troubling' becomes 'st' (I can't justify this - if you can you should believe this answer much more).
'primarily' indicates taking the first letters.
The initial letters of 'your eyelid' is 'ye'.
'st'+'ye'='STYE'
(Other definitions for stye that I've seen before include "Ocular inflammation" , "nasty spot" , "Inflamed swelling on the edge of an eyelid" , "Eyelid problem" , "Viewer's complaint" .)