The most common and most likely answer to this crossword clue is the 11 letter word ASTIGMATISM
I've seen this crossword clue in The Times
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Buddy explains!
The straight part
We know that "Vision problem" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case vision problem = astigmatism.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 ASTIGMATISM mean?
ASTIGMATISM noun- A defect of a lens such that light rays coming from a point do not meet at a focal point so that the image is blurred.
- A disorder of the vision, usually due to a misshapen cornea, such that light does not focus correctly on the retina causing a blurred image.