Because glasses can't protect you. Jk Rowling said in an interview. She said that "I had Justin protected by the camera lens, so I think I am open for criticism there, but the way I explained to myself he was looking through several lenses and wasn't actually seeing the thing directly, it wasn't through his eyeline, when you look through a camera you are looking through the lens, it is a little distorted"

If anything, the glasses would've made her see it more clearly, lol.

Justin wasn't protected by a camera lens, Collin was. Justin was protected by a ghost.

Seeing from glasses is seeing it directly.

As @Stxrannx said

He was looking through several lenses and wasn't actually seeing the thing directly, it wasn't through his eyeline, when you look through a camera you are looking through the lens, it is a little distorted.

Then how did Harry not die?????????