"Whatever I know about acting I've learned from being a stand-up comedian and from observing people," Newhart said. "When I read the script I knew who this guy was and knew what he was feeling -- that's kind of the criteria I use in accepting roles -- if I know the person and know I can portray him. If I'm not familiar with the emotion that person is going through, I'd probably pass."
In the "ER" episode, beginning Oct. 30, Newhart's character's lose of eyesight due to macular degeneration makes him question whether he wants to keep living, Zap2it.com reported.
"I kind of knew the frustration this guy had," Newhart said. "Everything he did was with his hands and the coordination with his hands and eyes, and now to be losing one of those senses, what that must be like."
The 74-year-old star of the "The Bob Newhart Show" and "Newhart" is healthy, which he attributes to good genes and the fact that he married the right woman, but he said he's familiar with losing an ability he could once do easily.