Mark 8:22-25:

And he cometh to Bethsaida; and they bring a blind man unto him, and besought him to touch him.
And he took the blind man by the hand, and led him out of the town; and when he had spit on his eyes, and put his hands upon him, he asked him if he saw ought [anything].
And he looked up and said, I see men as trees, walking.
After that he put his hands again upon his eyes, and made him look up: and he was restored, and saw every man clearly.

Notes on Mark 8:22-25:

You may have wondered if you’re the one doing the laying on of hands – is it a sign of unbelief to ask the person if he notices any improvement?  Jesus never walked in unbelief, and here He asked the man if he could see after He laid hands on him.  So this must be okay!  This also shows that it is valid to lay hands on the person a second time if the person does not confirm a total manifested healing the first time.  This does not mean, however, that a person should “believe he receives” a second time if the healing is not fully manifested.  Believing it once is sufficient.

See also:

Laying Hands on the Sick
Strange Ways to Get Healed
Get Away from Unbelief
Must We Lay Hands on the Specific Afflicted Body Part?
Is It Right to Get in a Second Healing Line for the Same Condition?
Is It Unbelief to Ask a Person You Laid Hands on Whether He Feels Better Yet?
Objection: Christ’s Healings Were Mostly Instantaneous; We Cannot Claim to Be Able to Do His Works When We Have So Few Instantaneous Miracles
Objection: The Lord Puts Us on Our Backs That He May Teach Us to Look Up
Condition: Blindness
Condition: Blurred Vision