Thanks for the replies, everyone.

The mail carrier did call the police and medics, so I was checked over on the spot and statements were taken from all concerned.

However, when I called the USPS....

I'm not sure what I was expecting - sympathetic treatment, maybe? Or some sort of apology?

Anyway - first thing I was told was that the incident was closed because I had left the scene too early!
They were surprised that I was even calling because, by not being there when their "investigation team" arrived on the spot, I had, apparently, absolved them of any responsibility for the incident (or something along those lines! I don't remember the exact wording they used, but it was exceptionally cold and heartless). I really did not have a clue what to say to this!

I got it together enough to point out that I had been told by the police officer on the spot that I was free to go and that the mail carrier didn't say or indicate that there was any reason for me to stay there, but the woman from the USPS just kept repeating that as far as they were concerned the incident was closed!

I'm not sure how we got there, but eventually she told me that she would send me a claim form, but that there was no obligation on their part because the incident was closed!

I've taken the bike to my lbs to get a crash-check (hopefully there will not be too much damage) and already bought a new helmet, but I'm going to have to live with the scratched glasses and throw away the clip-ons!

Hopefully I will get some more positive resonse from the USPS when I fill out the claim form!