Old friend stuck with nervous response of the eye (7)
I believe the answer is:
optical
'the eye' is the definition.
(I've seen this before)
'old friend stuck with nervous response' is the wordplay.
I cannot really see how this works, but
'old' could be 'o' (common abbreviation eg in OE for Old English) and 'o' is present in the answer.
'response' could be 'tic' (I have seen 'Involuntary response ' mean 'tic' so perhaps 'response' could also mean 'tic') and 'tic' is found within the answer.
'friend' could be 'pal' (pal can mean a friend) and 'pal' is present in the remaining letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'of' is the link.
Can you help me to learn more?
(Other definitions for optical that I've seen before include "Sighted" , "Relating to vision and light" , "Relating to light/vision" , "To do with sight, perhaps an illusion" , "Relating to the eye" .)