Problem of retina? Yes, possibly (9)
I believe the answer is:
eyestrain
'problem' is the definition.
(eye problem)
'retina? yes possibly' is the wordplay.
'possibly' indicates an anagram.
'retina'+'yes'='retinayes'
'retinayes' is an anagram of 'EYESTRAIN'.
'of' is the link.
(Other definitions for eyestrain that I've seen before include "Ocular tiredness" , "this could require attention from ophthalmologist" , "which makes it hard to see" , "Difficulty for reader" , "Reader's issue" .)