Having (a) 20/20 vision is the desirable condition of the eye.
If you have (a) 20/20 vision you don't need glasses.
(A) 20/20 vision is required for certain job positions.
Is the article "a" necessary or correct in these sentences?
I wanted to ask this question because sometimes I find the article "a" before "20/20 vision" and other times not. I'd like to know why.
You can find several examples on this ngram search, although the focus of this question is about the specific examples above.
"In that state you must have a 20/20 vision in one eye"
"A 20/20 vision is normal vision for distance"
"However, it is of interest that 35.9 per cent of those with a 20/20 vision and 40 per cent of those with a 20/30 vision complained of eye symptoms"
"...whereas commercial pilots are accepted if they have a 20/20 vision with correction"
" She has a 20/20 vision in the right eye by the use of a Schnelling's chart"
"First, the student, because he has a 20/20 vision as indicated by the test above, believes his vision is “normal”"
"Their report to applicant stated J. B. Pierce had a 20/40 vision of his right eye without glasses and a 20/20 vision of the same eye with glasses"