He could also get angry. Harry has shown that he can be fierce when his personal belongings, especially something as important as his glasses, are messed with. His anger might fuel his determination to get them back and also figure out who took them and why.
Perhaps he becomes more cautious and starts relying on his other senses more. He has been through a lot in his life, so he would likely adapt quickly. He might use his magic in new ways to compensate for his lack of clear vision, like using spells that can detect the presence of people or objects around him without having to see them clearly.
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.
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 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, 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.
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.
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.
In a fanfiction, if Harry Potter loses his glasses, the plot will likely take a different turn. His lack of clear vision could make him seem less confident, which would change how others perceive him. Enemies might underestimate him, giving him an opportunity to surprise them. His search for a replacement or a solution to his vision problem could introduce new characters, like an old wizard who specializes in eye - related magic, and new sub - plots could unfold as a result.
One possible reason could be as a form of humiliation. His enemies might take his glasses to make him feel vulnerable and less in control. Without his glasses, Harry is severely visually impaired, so it's a way to undermine his confidence.
On the other hand, he could feel ashamed. If he realizes that he has truly made a mistake, seeing his father so angry and disappointed could make him feel bad about himself. He might lower his head and not say anything, with a look of guilt on his face.
He might be initially in shock. Harry could stand there, unable to believe what has just happened. Then he might become angry, lashing out at his mate or the situation in general. He could say things he doesn't really mean in the heat of the moment.
He might be very sad at first. Harry has always valued his friends, so being forgotten by them would be a huge blow.