triathalon, includes a 15 meter swim through the hudson river, a 40 kilometer bike ride and 10 kilometer run through central park. >>gretchen: about a dozen athletes, believe it or not, are blind. anna kooiman joins us with a story of one of those athletes. >> they swim and run tethered to a guy. two let me tag along for training. check it out. >> 3, 2, 1. go. >> this is no normal bicycle built for two. amy is blind. caroline is her guide. >> i'm down to 1% of usable vision. >> it's the result of a rare inflammatory eye disease paired with glaucoma. >> i was do i go nosed when i was -- i was diagnosed when i was 22 years old. >> i'm with an organization i'm very passionate about.