Ocular tiredness (9)
I believe the answer is:
eyestrain
'ocular tiredness' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for eyestrain that I've seen before include "which makes it hard to see" , "Optic stress" , "What may give blurred sight" , "complaint" , "Tension on the visual organ" .)