Ocular tiredness (9)
I believe the answer is:
eyestrain
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">ocular tiredness</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(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" .)