After completing the filming of Star Wars, it's said that Mark Hamill was in a horrific car accident that nearly destroyed his face. The accident supposedly happened on January 11, 1977. It was never reported in the media (he wasn't very famous at the time) and no one seems to know where the crash occurred. In some accounts, Hamill has said "I broke my nose, that's it" and in others he claims the damage was more extensive.
It's very strange, though. If you watch his appearance on Mike Douglas from July of 1977, his face seems to me to be the same as it is in New Hope. In various other interviews from 1977 there doesn't seem to be much of a change. Then, in the 1978 Star Wars Christmas Special, he looks very, very bizarre. Pancake makeup, and he appears to be loopy, as if he's on painkillers.
In Empire Strikes Back, he does look different. His classically handsome/pretty visage was gone. His perfect roman nose was flattened, and his nostrils now asymmetrical. His eyes appear rounder, and there was a bit of weight gain. It's said that the Wampa attack at the beginning was meant to explain the change in his looks.
To me, in Return of the Jedi, six years after his accent he looks completely different. I remember watching it in the theater thinking "what happened to Luke?" He simply does not look like the same person as in New Hope. Also, it seemed to me he was even acting differently. His entire aura and countenance had changed. Beyond what it might have for character development reasons. I'm afraid that his Luke really takes a backseat to Han Solo, and Darth Vader. He didn't wind up to be very compelling.
I would speculate that after the accident, there were on-going problems. He claimed cartilage had been taken from his ear and used to reconstruct his nose. Is it possible that it worked at first and then was rejected. Because his nose looks ok to me in July, 1977, but looks very fucked up in Empire.
Or was there a second accident or incident that we're not privy to? Whatever happened, it seems to me it really shook him up.