Constant fiddling with lenses worn by daughter (7)
I believe the answer is:
endless
'constant' is the definition.
(thesaurus)
'fiddling with lenses worn by daughter' is the wordplay.
'fiddling with' indicates an anagram (I've seen this in other clues).
'worn by' is an insertion indicator (I've seen this in other clues).
'daughter' becomes 'd'.
'lenses' anagrammed gives 'enless'.
'enless' enclosing 'd' is 'ENDLESS'.
(Other definitions for endless that I've seen before include "Eternal - unbroken" , "Unceasing" , "Infinite, perpetual" , "Going on and on, interminable" , "Havin no limit" .)