Glasses almost needed for sight (9)
I believe the answer is:
spectacle
'for sight' is the definition.
(spectacle is a kind of sight)
'glasses almost' is the wordplay.
'glasses' becomes 'spectacles' ('spectacles' can be a synonym of 'glasses').
'almost' means to remove the last letter (most of the word but not all of it).
'spectacles' with its final letter removed is 'SPECTACLE'.
'needed' acts as a link.
(Other definitions for spectacle that I've seen before include "sensational event" , "Elaborate and remarkable display" , "of which a pair should improve 25 [SIGHT]" , "Lavish entertainment" , "Showy pageant" .)