Degeneration of retinas more unpleasant (7)
I believe the answer is:
nastier
'more unpleasant' is the definition.
('nasty' can be a synonym of 'unpleasant')
'degeneration of retinas' is the wordplay.
'degeneration of' indicates anagramming the letters (the original order of letters breaks down).
'retinas' with letters rearranged gives 'NASTIER'.
(Other definitions for nastier that I've seen before include "More disgusting" , "Less nice" , "Less pleasant" , "Retsina (anag) -- not so nice" , "More horrid" .)