One-ended pen cover for pupils (9)
I believe the answer is:
blindfold
'cover for pupils' is the definition.
(as in pupils in your eyes)
'one-ended pen' is the wordplay.
'one-ended' becomes 'blind' (as in a blind alley).
'pen' becomes 'fold' (fold is a kind of pen).
'blind'+'fold'='BLINDFOLD'
(Other definitions for blindfold that I've seen before include "Piece of cloth etc to prevent one seeing" , "bandage" , "headband" , "Unable to see" , "Stop one looking" .)