Reading issue certainly present in European school (9)
I believe the answer is:
eyestrain
'reading issue' is the definition.
(problem that may be caused by reading)
'certainly present in european school' is the wordplay.
'certainly' becomes 'yes' (both can be used to answer in the affirmative).
'present in' indicates putting letters inside.
'european' becomes 'E' (abbreviation e.g. EU).
'school' becomes 'train' (training is a kind of schooling).
'e'+'train'='etrain'
'yes' placed into 'etrain' is 'EYESTRAIN'.
(Other definitions for eyestrain that I've seen before include "Reader's issue" , "Stress on mince pies (in the East End)?" , "You're looking too hard for this" , "Optical irritation or tiredness" , "It might cause pupils problem" .)