Piggy's glasses may be seen as symbolic for several reasons. One is that they are a reminder of Piggy's weak physical condition relative to the other boys, "My specs!" howled Piggy. "Give me my specs!"......"Jus' blurs, that's all. Hardly see my hand-" (p. 53).
The glasses are also a symbol of power. Whoever has the glasses will have the all-important ability to make fire. Jack and his gang use violence to take the glasses and thus empower themselves whilst disempowering Ralph and his remaining group.
Piggy's one eyed view of the world is also symbolized after the glasses are damaged. He doesn't share in the excitement the other boys feel about being on the island and is only able to view the world through the prism of an adult's perspective. This alienates him from most of the group.
Piggy's glasses are probably the most prominent symbol in the novel.