Eyes

the only parts of the body the same size at birth as they'll always be. "That's why all babies are beautiful," Thurber used to say as he grew blind -- not dark, he'd go on to explain, but floating in a pale light always, a kind of candlelit murk from a sourceless light.

He needed dark to see: for a while he drew on black paper with white pastel chalk but it grew worse.

Light bored into his eyes but where did it go?

Into a sea of phosphenes, along the wet fuse of some dead nerve, it hid everywhere and couldn't be found.

I've used up three guesses, all of them right.

It's like scuba diving, going down into the black cone-tip that dives farther than I can, though I dive closer all the time.