Eye complaint among the worst yet (4)
I believe the answer is:
stye
'eye complaint' is the definition.
(I've seen this before)
'among the worst yet' is the wordplay.
'among' indicates the answer is hidden within the clue.
'STYE' is hidden in the letters of 'worst yet'.
(Other definitions for stye that I've seen before include "Red eye" , "Viewer's complaint" , "Swelling near the eye" , "Eye sore" , "Eye blemish" .)