Almost lose one's sight seeing demon (6)
I believe the answer is:
goblin
'demon' is the definition.
(thesaurus)
'almost lose one's sight' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'lose one's sight' becomes 'goblind'.
'goblind' with its final letter taken away is 'GOBLIN'.
'seeing' acts as a link.
(Other definitions for goblin that I've seen before include "Naughty sprite" , "Little monster" , "Mischievous sprite" , "Evil imp" , "nasty little thing" .)