Sight defect (6,6)
I believe the answer is:
tunnel vision
'sight defect' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for tunnel vision that I've seen before include "Seeing problem" , "Narrowness of viewpoint" , "unwavering concentration? - with 4a" , "dream Napoleon had for invading England?" , "Condition where one can only see objects directly ahead" .)