The most common and most likely answer to this crossword clue is the 8 letter word CATARACT
I've seen this crossword clue in The Guardian
C
A
T
A
R
A
C
T
More clues leading to the result CATARACT
- What may prevent you seeing waterfall?
- Fall that could lead to blindness
- Problem seeing pet carrying a little weight around
- Waterfall is a problem for sightseers
- Trouble in sight of cascade
- Cause of cloudiness that affects visibility in fall
- Visual impairment caused by falls
- Viewer’s complaint about diplomacy engaging Arab
- Many locally see you engaged in deed that may cause blindness
- Downpour makes it hard to see
Buddy explains!

The straight part
We know that "Viewer’s complaint" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case viewer’s complaint = cataract.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CATARACT mean?
CATARACT noun- A waterspout
- A large waterfall; steep rapids in a river.
- A flood of water
- An overwhelming downpour or rush
- A clouding of the lens in the eye leading to a decrease in vision.