[Rndouglas]

Also, when Frodo and Bilbo turned invisible, surely they would have gone blind, as their retinas were invisible, so therefore couldn't pick up light?

Ah well, you see, the property of the ring was to actually bend light around the person wearing it which effectively made the wearer invisible to other people. The light bending effect also causes a vision impairment to the wearer, hence the strange view they have of the world whilst wearing the aforesaid ring. Twas ever thus in days of yore whilst strange creatures roamed the world and much evil was upon the land. Only men of great fortitude and moral uprightness could hope to stand against such evil and hope, perchance, to prevail. Let this be a rallying cry to all men good and true.

Sorry, got carried away.