New topic relating to vision (5)
I believe the answer is:
'relating to vision' is the definition.
(I've seen this in another clue)
'new topic' is the wordplay.
'new' indicates an anagram.
'topic' anagrammed gives 'OPTIC'.
(Other definitions for optic that I've seen before include "Eye - spirit measure" , "Device for measuring out spirits" , "Ocular" , "What could measure the spirits" , "Of sight or the eye" .)