Organ of sight (3)
I believe the answer is:
eye
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">organ of sight</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for eye that I've seen before include "Ireland's . . ., off the Dublin coast" , "Symmetrical spot" , "Look at, scrutinise" , "Place for pupil" , "where the pupil is seated" .)