All round, the London one has a focus of attention (3)
I believe the answer is:
'attention' is the definition.
(I know that eye is a type of attention)
'all round the london one has a focus' is the wordplay.
'all round' says the letters should be written in reverse (all the words are reversed).
'the london one' becomes 'ye' (I can't explain this - if you can you should believe this answer much more).
'has' is a charade indicator (letters next to each other).
'a' becomes 'per' (eg 'one a day' means 'one per day').
'focus' indicates the central letters (focus can mean the centre of something).
The middle letter of 'per' is 'e'.
'ye' written backwards gives 'ey'.
'of' is the link.
Can you help me to learn more?
(Other definitions for eye that I've seen before include "It accommodates a pupil" , "Centre of storm" , "Observer" , "'Public' or 'private' body part" , "Twenty four ac emphasises it" .)