Describes clear vision for this pair of numbers (12)

I believe the answer is:

twentytwenty

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

'describes clear vision for' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.

'pair of numbers' is the wordplay.
'pair' shows that letters should be duplicated.
'of numbers' becomes 'twenty' (I can't justify this - if you can you should believe this answer much more).
'twenty' doubled is 'TWENTYTWENTY'.

'this' acts as a link.

Can you help me to learn more?

I've seen this clue in The Irish Times.

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