A symptom of those with second sight? (12)

I believe the answer is:

doublevision

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'a symptom of those' is the definition.
I can't judge whether this defines the answer.

'with second sight?' is the wordplay.
'with second' becomes 'double' (I can't explain this - if you can you should give a lot more credence to this answer).
'sight?' becomes 'vision' ('vision' can be a synonym of 'sight').
'double'+'vision'='DOUBLEVISION'

Can you help me to learn more?

I've seen this clue in The Irish Independent.

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