I work with an engineer who is visually challenged and uses emacs with dictation to code. He is a pretty phenomenal engineer.
The average person is just average. Unless there is something about visual impairment that makes them better at development, then I would expect them to be on average, just average developers.
Yet I would guess that visually impaired developers get more scrutiny. If nothing else, just because they are a novelty.
Anyhow, I guess I am just reminding myself to treat each person as an individual.