how does the theme relate to piggy's specs?

A theme is an underlying message or idea that the author is trying to convey. Piggy is intelligent and perhaps the boys' best resource to help them get off the island. They, however, bully and humiliate him. Piggy's glasses are really an extension of Piggy and part of the theme of intelligence being waisted, and even destroyed, on the island. Piggy's glasses even serve a functional role on the island as their only way to start fire. Recall when Jack is angry, he hits Piggy and shatters a glass. That's 50% of their fire gone!