Display more than one to improve vision (9)
I believe the answer is:
spectacle
'display' is the definition.
(I know that spectacle is a type of display)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for spectacle that I've seen before include "of which a pair should improve 25 [SIGHT]" , "Picture" , "Remarkable sight" , "sensational event" , "Showy pageant" .)