Cascades (9)
I believe the answer is:
cataracts
'cascades' is the definition.
('cataract' can be a synonym of 'cascade')
This is all the clue.
(Other definitions for cataracts that I've seen before include "Eye problems causing blurred vision" , "Waterfalls and eye diseases" , "Large waterfalls and eye defects" , "Eye afflictions produce waterfalls" , "Waterfalls in the eyes?" .)