OAK CREEK, Wis. — Hold an empty toilet paper roll to your eye and peer through it. Your view is confined to what’s at the end of a narrow tunnel smudged by shadows.

For almost eight years now, ever since he took a ding to the side of the head in a Division III college football game, that’s how Justin Greenwood has seen the world. His thick glasses with their prisms on the sides help, giving him peripheral vision — “They’re like rearview mirrors on your car.” But, at 29, he is legally blind.

He golfs and skis, but cannot drive a car. He travels on his own, but uses a cane to help him navigate the uneven terrain and obstacles in his way when he goes somewhere unfamiliar. He reads books and works puzzles, but struggles with his memory.

And his dreams of playing professional football or using that marketing degree he was working toward when he got hurt are over, replaced by a desire to protect other youngsters from a similar fate.

“What’s good about me is I can laugh about it. A lot of people can’t accept the life they have now,” said Greenwood, an eternal optimist with an infectious smile. “A big part of it is acceptance with this life. I have to accept my challenges and my difficulties and my inability to do the same things people around me are doing.

“It’s challenging, but it’s doable.”

It’s a situation that also is preventable.

Greenwood has become an ardent advocate of brain injury awareness since he got hurt, and is the spokesperson for the new “Play Smart Wisconsin” campaign. While he’d never tell anybody not to play football — or any other sport, for that matter — he hopes his experience will teach kids why it’s important to be honest about injuries as soon as they happen.

He also wants to make sure coaches are teaching proper technique and following guidelines that keep players with head injuries off the field until they’re cleared by a medical professional. There needs to be adequate medical staff at all games, too, so kids who do get hurt get immediate treatment.

The nephew of David Greenwood, a safety at Wisconsin who played three years in the NFL, Justin Greenwood was a standout athlete. He once pitched a no-hitter for his high school team and qualified for the state finals in track and field the same day. In the fall of 2003 he was a junior at the University of Wisconsin-Eau Claire, playing linebacker and special teams.

“I was the wedgebreaker on kickoffs. I’d come down and just, ‘POW!”‘ Greenwood said.

He suffered a stinger during the second game of that season, but didn’t think much of it. Oh, he might have had some headaches in the days that followed. But he couldn’t even tell you when he got hit, and he never mentioned it to his mother or any of his coaches. He certainly didn’t think about sitting out the next game.

But the hit had made the vascular system in his brain “really, really, really weak and fragile.” So much so that when Greenwood took a minor hit on the side of his head during a kickoff return Sept. 27, 2003, it nearly killed him.

Blood vessels in his brain ruptured, shattering the fragile network of connections that keeps the human body working. Disoriented, Greenwood made his way to the sidelines and threw up. He wobbled and swayed as he talked to the trainer, then collapsed. Though there was a physician at the game, there was no ambulance and, thus, no way to immediately clear an airway and keep precious oxygen flowing to Greenwood’s brain.

“They almost didn’t operate on me,” he said. “My eyes responded to light the second time, that’s why they did surgery. Otherwise, they would have pronounced me dead on the doctor’s table right there.”