There is a lot of "darkness" in the story. The "darkness" in the story of Heidi produces blindness. Some of that blindness is temporary and fixable. Some is not.
The only person in the story who is physically blind is "the grandmother." She isn't Heidi's grandmother. She is Peter's (the goatherd neighbor boy) grandmother.
Peter is only a little older than Heidi. Each morning he takes his and Heidi's grandfather's goats up to the high pasture to graze.
"The grandmother" is old and blind. When she first meets Heidi, she runs her hands and fingers very carefully over Heidi's face so she can "see" Heidi. She "sees" with her fingers.
A blind person can "see." Blind people actually talk about "seeing." It is startling to hear a blind person talk about "seeing." Some blind people actually see more clearly than many sighted individuals.
Most of the people in Heidi are blind in some way. But there are at least three people in the Heidi story who see pretty clearly. One of them is Peter's grandmother. She sees Heidi's heart and encourages Heidi to cast her light and love near and far. Heidi and Clara's grandmother are the other two people who can "see.""The grandfather" lives in darkness and isolation because he chooses to do so. He knows the pain of loss, and he has put up a tall wall around his heart to protect it from further hurt. In the process he is hurt in all kinds of ways. He makes a regular practice of lashing out at anyone who tries to be kind just because he is protecting his heart.
Peter is "blind," too. Peter thinks that love has to be hoarded. He doesn't understand until the end of the story that love blooms when it is shared and even given away.
Clara is Heidi's city friend. Heidi goes to live with Clara as her companion. Clara is frail and spends her days in a wheelchair. Clara is "blind" because she is selfish and totally self-absorbed. Before the story is over, Heidi reaches Clara's heart and dispels the darkness there.
There are others with sight issues in the story: Clara's father is one. Most, if not all of them, are eventually touched by Heidi's love.
Heidi found the secret to pushing back darkness: it happens one heart at a time!
As I grow older, my eyes don't work as well as they once did. Christmas day I found myself trying to read a story to the people assembled around our dining room table. I didn't have my glasses, and I didn't want to interrupt the moment to get them. Once I started reading, I realized that I wasn't seeing well at all. It was scary! I got through the story but it was extremely challenging. I just don't see as well as I once did.
However, living without sight is much less risky and scary really than living with a blind heart! God knows that which is why He's in the business of restoration - one blind heart at a time!
There are a number of places in the Bible that talk about God seeing and even about God's eyes. One of my favorites is 2 Chronicles 16:9: "The eyes of the Lord range throughout the earth to strengthen those whose hearts are fully committed to Him. ... "
Put a little differently: God is always looking for restored (or being restored) hearts willing to do whatever it takes to love, serve and obey Him. Those are the hearts God uses to do His work! God sees and uses hearts - not perfect hearts - but hearts (and people) who know how greatly they need God's loving restoration. God goes to any length to seek out such servants and promises to strengthen them for the task of building His Kingdom.
Heidi's grandfather was afraid to trust and to love. It was just too risky! It just seemed safer to push people away and live without love all alone behind his self-constructed wall.
We fear the same vulnerability for the very same reason - the risk of pain and loss. We even push God away. We miss the truth that He is looking (with His eyes of love) for hearts that trust Him and are committed to Him. The Father delights in being strong when we are weak or scared. The Father delights to see our hearts and to work there to produce restoration. When we know and experience God's acceptance and love, then we are more willing to risk in relationship with other people - one heart at a time.