I think the following would be "more comprehensible," meaning more people who read it would understand ... only 10 nerve cells are involved in viewing a dime held at arm's length.
“viewing a dime held at arm’s length” — perfect. No ambiguity there. That’s the old standby explanation.
I’m nitpicking, of course. Otherwise it’s a fine, and very interesting, article. It really illustrates how little we know about the wonders of vision (which rather surprised me).