In this fanfiction, his glasses could have a disorder where they constantly fog up, no matter the temperature or humidity. It would be really annoying for Harry. He might be in the middle of a battle with Death Eaters or trying to solve a mystery in Hogwarts, and he has to keep wiping his glasses to see clearly.
The glasses could have a disorder where they start multiplying. So Harry wakes up one day and finds he has dozens of pairs of glasses all over his bed. They could be different sizes and shapes too. This would be really confusing for him, especially when he's in a hurry to get to class or go on an adventure.
It could slow down the plot. For instance, if Harry's glasses are constantly malfunctioning, he might miss important clues or signals. This would add more obstacles to his journey of solving mysteries or fighting against the dark forces.
Maybe Draco takes the glasses as a form of teasing. He shows them off to his Slytherin friends. But then, Hermione catches him with the glasses and scolds him. Draco, not wanting to be seen as a bully in front of Hermione (who he might secretly respect), decides to return the glasses. This could lead to a more complex relationship between Draco, Harry, and Hermione in the fanfiction.
Harry could be at a significant disadvantage without his glasses. He might misjudge distances when Nagini attacks, making it more dangerous for him. However, this could also lead to the discovery of new magical abilities, like a form of magic - based echolocation. Nagini might be used by the dark forces to take advantage of Harry's impaired vision.
It could be that the glasses represent more than just a visual aid for Harry. Maybe they are a symbol of his identity as 'Harry Potter, the Boy Who Lived'. In the fanfiction, the realization might be part of a deeper exploration of how his appearance and the items associated with it are intertwined with his destiny. For example, his glasses could be a connection to his past, perhaps having some magical origin or significance that he was previously unaware of.
He could try to trick the Snatchers into giving them back. Maybe he pretends to be more injured or incapacitated than he really is, and when they come close to check on him, he quickly grabs his glasses back.
Another plot development could be related to his family. Harry might find out that the glasses were passed down from his parents or some other important family member, and there is a family secret or power associated with them. This could involve a quest to learn more about his family's past and the true nature of the glasses, which could put him in conflict with some dark forces that don't want him to uncover the truth.
In the fanfiction, if Harry Potter's glasses were confiscated, he would be at a huge disadvantage. His ability to observe his surroundings, which is crucial in the wizarding world full of hidden passages and magical creatures, would be severely hampered. Without his glasses, he might not be able to recognize friends or foes quickly. Also, during Quidditch, he wouldn't be able to see the Snitch clearly, and his team could lose the game.
He could misidentify people. Maybe he mistakes a Slytherin for a Gryffindor and gets into an awkward situation. It would be a humorous scenario where he has to quickly correct himself.
It could symbolize his vulnerability. Without his glasses, Harry can't see clearly, which makes him more defenseless in this chained - up situation.
One possible plot could be that without his glasses, Harry discovers he has a new magical ability related to his vision. Maybe he can see magical auras more clearly and it helps him in his fight against the dark forces. For example, he can easily detect hidden Death Eaters by the color of their auras.