Crossword Genius

Problem with vision producing fall (8)

Ross

I believe the answer is:

cataract

I'm a little stuck... Click here to teach me more about this clue!

'fall' is the definition.
(I've seen this before)

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 "It may prevent someone seeing" , "Waterfall - eye problem" , "A real downpour" , "Cascade; eye defect" , "Falls" .)

I've seen this clue in The Guardian.
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