Therefore said they unto him, How were thine eyes {c} opened?

(c) This is a Hebrew idiom, for they call a man's eyes shut when they cannot receive any light: and therefore blind men who are made to see are said to have their eyes opened.

Matthew Henry's Concise Commentary

9:8-12 Those whose eyes are opened, and whose hearts are cleansed by grace, being known to be the same person, but widely different in character, live as monuments to the Redeemer's glory, and recommend his grace to all who desire the same precious salvation. It is good to observe the way and method of God's works, and they will appear the more wonderful. Apply this spiritually. In the work of grace wrought upon the soul we see the change, but we see not the hand that makes it: the way of the Spirit is like that of the wind, which thou hearest the sound of, but canst not tell whence it comes, nor whither it goes.