Crossword Genius

An aid to vision to work on vacant girl and fool (5-5)

Ross

I believe the answer is:

opera-glass

I'm a little stuck... Click here to teach me more about this clue!

'an aid to vision' is the definition.
I know nothing about this answer so I can't judge whether this works.

'work on vacant girl and fool' is the wordplay.
'work on' becomes 'opera' (I've seen this before. I am not sure about the 'on' bit.).
'vacant' says to hollow out the word (remove centre letters).
'and' is a charade indicator (letters next to each other).
'fool' becomes 'ass' (both can mean a stupid person).
'girl' with its middle taken out is 'gl'.
'opera'+'gl'+'ass'='OPERA-GLASS'

'to' acts as a link.

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.
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