Falls that can impair one's vision (8)
I believe the answer is:
cataract
'falls' is the definition.
(synonyms)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for cataract that I've seen before include "can obstruct your view" , "may impair the vision" , "Waterfall - opacity of the eye" , "A real downpour" , "(Nile) waterfall" .)