Go for one accountant with line of sight (7)
I believe the answer is:
optical
'of sight' is the definition.
(optical means relating to sight)
'go for one accountant with line' is the wordplay.
'go for' becomes 'opt' (to go for something is to opt for it).
'one' becomes 'i' (Roman numeral).
'accountant' becomes 'CA' (abbreviation for chartered accountant).
'with' is a charade indicator (letters next to each other).
'line' becomes 'l' (used when specifying particular lines from a poem).
'opt'+'i'+'ca'+'l'='OPTICAL'
(Other definitions for optical that I've seen before include "Relating to vision and light" , "Coal tip (anag)" , "Relating to the eye" , "Concerned with view" , "Relating to light/vision" .)