Former Marine Steve Walker has lost his vision, but not his iron will to become an Ironman triathlete

Steve Walker always wanted to be a Marine. But after becoming one, he noticed his sight began to deteriorate, little by little. By the time he left the Corps he was legally blind. Now 31, Walker has just 5 percent of his sight left, and that could soon be lost. What hasn't been lost is his drive to feel alive and accomplish goals. This Saturday he'll do a half-Ironman triathlon in Oceanside, and in the fall he'll do a full Ironman in Cozumel, Mexico. Someday, he wants to do the granddaddy of them all in Kona, Hawaii. My story for ESPN.com's Endurance Sports section: http://espn.go.com/sports/endurance/story/_/id/10683105/endurance-sports-blindness-stopping-former-marine-steve-walker