Seeing problem certainly in damaged retina (9)
I believe the answer is:
eyestrain
'seeing problem' is the definition.
(problem which affects one's seeing)
'certainly in damaged retina' is the wordplay.
'certainly' becomes 'yes' (I've seen this before).
'in' means one lot of letters goes inside another.
'damaged' is an anagram indicator.
'retina' anagrammed gives 'etrain'.
'yes' inserted within 'etrain' is 'EYESTRAIN'.
(Other definitions for eyestrain that I've seen before include "It might cause pupils problem" , "Tension on the visual organ" , "Optic stress" , "Eat resiny mix to cause optical pressure" , "Stress on mince pies (in the East End)?" .)