Derek Smith doesn't think it's a big deal and doesn't want it to be a big deal to anyone else.

If the Chargers' newest inside linebacker turns out to not be everything you think he should be, blame his 33-year-old legs or whatever else.

But don't mention the eye.

“It isn't an issue,” Smith said. “I'm over it. . . . I don't want there ever to be an excuse – 'Oh, his eye is bad.' ”

Smith, a San Diego resident since 2004, will get his first game action as a Charger in tomorrow night's exhibition opener against the Dallas Cowboys, working mostly with the second-team defense. By the season opener, he will be starting.

Smith was signed in February – agreeing to terms less than a week after the San Francisco 49ers released him – for two years and slightly more than $2.5 million. The move was believed at the time to be solely for depth behind Matt Wilhelm and Stephen Cooper. The signing proved prescient when it was subsequently learned that Cooper would be suspended for the first four games of the season for a failed drug test.

While Anthony Waters could push for playing time in September and beyond, Smith is almost certainly who will be on the field in place of Cooper. The Chargers knew of Cooper's positive test in February. While Smith was signed for experienced depth, he was also signed to start these four games.

Despite his protests, that Smith is playing at all is remarkable.

His eye is mostly fine now.

Sitting in front of his locker, looking up, he demonstrates the only time he has trouble. When he tries to see at a certain angle, his left eye has trouble tracking. It's barely perceptible.

“If I were a receiver,” he said, “it would be really bad.”

He's not. He just has to tackle people.

In 2006, he had to do it while seeing two of everyone. Smith played that entire season with double vision and distorted depth perception.

While Smith began to see double in the second game and within a few weeks was seeing double every waking moment, he played in all but three games. And he missed those because of a hamstring injury, not the eye.

The 49ers' leading tackler every season from 2001 to 2005, Smith still had 93 tackles that season. He had to hold his head at a cocked angle to even be able to see well enough to play.

“It affected my reads, tackling, everything,” Smith said.

He spent many Tuesdays – players' off day – visiting different specialists. At one point, it was thought he might have had a stroke.

Doctors never did figure out exactly what happened. It is believed Smith was hit in the head from behind in practice before the season opener and had the force of the hit traumatize his eye.

The remarkable thing is that Smith is so unaffected by the experience.

He said he never considered not playing during the '06 season and only briefly wondered if he'd play again after surgery to repair his vision in February 2007. Doctors told him he could not make the injury worse. The damage was done. Smith said he had no problems with the eye last season.

So, of course, he is still playing.

“I love it,” he said of football. “I have a lot fun doing it. If you still love what you're doing and you can physically do it, why not?”

Smith started 14 games and had 98 tackles for the 49ers last year but was due to make $4.5 million in 2008. His release was a foregone conclusion.

But he is unsure if he would have continued to play if the Chargers weren't interested.

“You get to a certain point in your career and you want to win a championship,” Smith said. “This seemed like a good place to try to do that.”

Nuts 'n' Bolts

 Tomorrow's game will be televised live in Southern California after enough tickets were sold for the game to be considered a sellout. The Chargers had received a 24-hour extension to sell about 500 remaining tickets.

 The Chargers will wear their alternate (powder blue) jerseys Oct. 12 against New England and Dec. 4 against Oakland. The Oct. 12 game is also alumni day and will feature Fred Dean's induction into the team's Hall of Fame.

 Just three open training camp practices remain (4-6 p.m. Monday, Tuesday and Thursday). But already more fans have watched training camp workouts this year than in any of the previous three held at Chargers Park. More than 24,000 fans have watched 11 practices this year.

 It seems sure that Luis Castillo (back), Scott Chandler (back), Marcus McNeill (neck) and Cory Withrow will miss tomorrow's game. All have missed multiple practices, including yesterday's.

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Kevin Acee: (619) 293-1857; kevin.acee@uniontrib.com