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This is blue; this is red, exclaimed Thomas Martinelli, showing off his candy.

Ring pops are the way to the heart of this four-year-old, who like so many of his peers find that a little bit of sugar and race cars go a long way.

But behind this kind soul is a large unknown.

It is hard to explain, because it is not tangible; they don't see anything different about him, said Thomas' mom, Kim Martinelli.

When he was 19 months old, Thomas' parents found out he has retinitis pigmentosa, an inherited, degenerative eye disease. That means one day, Thomas eyesight is expected to fail.

His bright world of colors and his mom's smile will go dark.

His resolve is unbelievable. He doesn't know how it is to have normal vision, said his dad, Brent.

I'm going to help you by holding your hand... here we go, Kim said as she helped Thomas practice using a cane in their front yard to help deal with with his tunnel vision... and to prepare for the future.

When he is looking ahead, he is not catching anything on the ground, his mother explained.

At home and at school, Thomas is learning to read braille.

The Martinelli home is getting new paint to help Thomas' depth perception. The steps out front are bright orange to warn him a change is coming.

Lights have extenders.

And his room is always on a dimmer, because Thomas is night blind.

Thomas acknowledged that it's hard to walk with a cane, but he has plenty of support, especially from his little brother Gage, who told he dad that he, too, wanted a cane.

Researchers are working on answers to the mystery behind retinitis pigmentosa, and the Martinellis have great hope that science will outpace Thomas' vision loss.

There is still a little hope that we won't get there, Kim said

E-mail sslater@wfaa.com

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