Light-sensitive membrane (6)
I believe the answer is:
retina
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">light-sensitive membrane</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 retina that I've seen before include "Ocular membrane" , "What's behind the humour" , "Membrane covering the back of the eyeball" , "Sensitive layer in eye" , "Eye's membrane" .)