I've noticed that one of the headlights in my Ford Focus has become opaque. However, this doesn't seem to match with what people call "foggy" or "hazy headlights": not only the fog is not evenly spread (it's more of a "stain"), but it really looks like it is the inside of the lens that got opaque, not the outside.
Some friends suggested that the lamp may not be the right one, and that it gets too hot and burns the plastic. However, I didn't change the lamp myself when it broke, but I had it changed in a shop. Also, the same shop changed the lamp in the other headlight, which is fine instead. Some suggested that maybe when the previous lamp broke it sent out a quick burst of heat which caused the damage.
It is more of a side stain, it doesn't sit in front of the lamp and it doesn't seem to affect the projection of the light, however some people suggested that it might be an issue for the next mandatory inspection (I live in Italy). Anyway, it's a bit ugly, and I would really rather fix that.
Is it possible that the damage is on the inside? If that is the case, do I have any other choice than to replace the headlights?
Thanks in advance.
EDIT Here are a few pictures of the headlight (they're a bit dirty, sorry about that, but the issue is quite visible):
For reference, here is a picture of the other headlight: