Unfortunately I broke my specs today which I used in this question.
But I observed that the edges are completely different then the entire part of the lens. The middle portion of the lens was completely transparent but the edges appeared opaque (and I can't see through the edges). This image shows the same in case of a shattered glass.
The edges in the above picture are green and not transparent as other portions appear.
So why are the edges not transparent (in both the case of specs and the shattered glass)?
Edit : I would like to add that the edges of my specs were not green. They were just silvery opaque. I couldn't take a pic of it during asking the question but take a look at it now.
Best Answer
Because you're looking through more of glass
I'd like to just add to the other answers with some diagrams. We have an intuition that light beams travel in straight lines, so we tend to assume that the beam paths looking through glass might be as follows:
However, the actual paths of the beam due to refraction and total internal reflection look more like this:
Note that the beams that enter the face of the glass aren't significantly deflected, and exit the glass pretty quickly. However beams that enter the edge of the glass spend a lot more distance within the glass. As the beam spends more time within the glass, it has more of a path to be affected by impurities.