Harry could be a bit more laid - back about it at first. He might make a joke about Draco looking silly while squinting with his glasses. But as time passes and he realizes he really needs his glasses, he gets more serious and starts to plot a way to retrieve them without getting into too much trouble with the school authorities.
Harry could be really angry. He might immediately try to get his glasses back, using some basic spells or just by physically trying to grab them from Draco. He'd be frustrated that Draco is always causing trouble for him.
Well, Harry could also be more level - headed. He might try to figure out Draco's motive first. Since he's used to Draco's antics, he could choose to outwit Draco instead of getting into a physical or shouting match. He could use magic in a clever way to get his glasses back without causing too much of a scene.
One possible motive could be that Draco wants to annoy Harry. Stealing his glasses is a petty way to get under his skin. It's a simple act of mischief that Draco might think is funny. Another reason could be that Draco is jealous of Harry. By taking something so important as his glasses, he feels like he has some power over Harry.
Harry might initially be in a state of shock. He has always been able to rely on his glasses to see, and without them, the world is a blur while he's being tortured. This could make him angry too. He might lash out blindly, trying to cast spells in the direction he thinks his enemies are, even if he's not sure. And as the torture continues, he could become more determined to resist, using his strong willpower to endure the pain and fight back in whatever way he can.
He might be initially panicked. Since his glasses are essential for him to see clearly, not having them would make him feel very vulnerable and exposed in a dangerous wizarding world.
He might be very frustrated. Without his glasses, he can't see well, which is a big handicap for him. He could be trying to use his other senses more acutely, like listening for any approaching footsteps or voices. He might also be thinking of ways to break free from the bindings using some basic spells he can do without clear vision, like a simple levitation charm to try and reach for his glasses if they're nearby.
Well, it could be that Draco steals Harry's glasses as a prank. Maybe he wants to embarrass Harry in front of their classmates. He might hide the glasses in a secret place in Hogwarts, like in an old unused classroom, and Harry has to search for them while dealing with his blurry vision.
One possible reason could be to annoy Harry. Draco is often portrayed as a bully in the Harry Potter series, and stealing Harry's glasses is a way to make his life difficult. It could also be a power play, showing that Draco can take something important from Harry.
Harry could be initially shocked and hurt. After all, having your potential mate reject you is a very painful experience. He might start to question himself and wonder what he did wrong. Then, he could become angry. Given his Gryffindor nature, he might confront Draco about the rejection and demand an explanation.
Some characters would react with shock. For example, Ginny would be outraged that someone would do such a thing to Harry. She would be ready to fight whoever was responsible. Luna, in her unique way, might see it as an interesting new state for Harry. She could offer some of her strange but useful magical items to help him. And a Hogwarts teacher like McGonagall would be strict about finding out who was behind it. She would also make sure Harry was taken care of, ensuring he had proper assistance in getting around until the situation was resolved.
Harry might initially be very angry and hurt. He could cut off all communication with Draco and become withdrawn. In some fanfics, he would even start to avoid places where he might run into Draco.