Viewer allows openings (7)
I believe the answer is:
eyelets
'openings' is the definition.
(eyelet is a kind of opening)
'viewer allows' is the wordplay.
'viewer' becomes 'eye' (I've seen this before).
'allows' becomes 'lets' ('let' can be a synonym of 'allow').
'eye'+'lets'='EYELETS'
(Other definitions for eyelets that I've seen before include "Rings for reinforcement" , "peep-holes" , "Small holes" .)