The difficult word here is “of”, which needs to be understood in the sense “by”:
> **of, _prep._ 14.** Introducing the agent after a passive verb. The usual word for this is now _by_ , which was prevalent by the 15th cent.; _of_ was used alongside _by_ until c1600. _Of_ is subsequently found as a stylistic archaism in biblical, poetic, and literary use
>
> _Oxford English Dictionary_.
So Dickinson means that the road is enabled _by_ the eye: that is, the road is enabled to be seen by the eye (imagination) of the poet.
Other poems where Dickinson uses this archaic sense of “of” are ‘I cannot live with You’:
> Like a Cup—
> Discarded **of** the Housewife—
and ‘There is a Shame of Nobleness’:
> A finer Shame of Ecstasy—
> Convicted **of** Itself—