Inadvertent mistake as regards vision (9)
I believe the answer is:
oversight
'inadvertent mistake' is the definition.
(I've seen this before)
'regards vision' is the wordplay.
'regards' becomes 'over' (I can't explain this - if you can you should believe this answer much more).
'vision' becomes 'sight' ('sight' can be a synonym of 'vision').
'over'+'sight'='OVERSIGHT'
'as' is the link.
Can you help me to learn more?
(Other definitions for oversight that I've seen before include "error" , "A failure to notice, an omission" , "Shot giver due to unintentional omission" , "Carelessness" , "Supervision - omission" .)