I thought it was pretty obvious....after Gollum fell into Mt. Doom, he did the impossible: yes, he adapted to the life inside lava. The Ring was actually not completely unmade: its power was transferred to Gollum. Now, Gollum, with the Ring's power, not only survived, but became powerful. He managed to climb out of the lava, but half of his body had melted so that he looked like a slug.
Yes...Gollum, after his years of drinking lava, became fat...he IS Jabba the Hutt. As the Ring's power passed into him, his eye...well, you get the idea
