The most common and most likely answer to this crossword clue is the 6 letter word OCULAR
I've seen this crossword clue in Independent
O
C
U
L
A
R
More clues leading to the result OCULAR
- Funnything astronomer looks into
- Some jocularity concerning sightseers, perhaps
- Compose carol about start of unity of vision
- Skip start of funny visual
- Eye-related article, in colour, about ditching Boris’s no. 2
- False religion briefly embroiled in row about vision
- Funny top out of sight
- Like the Eye, inclined to jest? No honour in that
- Funny when Jack leaves mince pie
- Pupils can present such a problem
Buddy explains!

The straight part
We know that "of vision" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case of vision = ocular.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 OCULAR mean?
OCULAR noun- The eyepiece of a microscope or other optical instrument.
- Any of the scales forming the margin of a reptile's eye.
- Of, or relating to the eye, or the sense of sight
- Resembling the eye.
- Seen by, or seeing with, the eye; visual.