Flyers star defenseman Chris Pronger will visit with two Pittsburgh concussion specialists on Wednesday, and the club hopes they can explain the cause of his headaches.

A local doctor on Monday said a blow to the eye - which Pronger suffered on Oct. 24 against Toronto - can cause a concussion.

After taking an inadvertent stick to the eye and missing six games, Pronger returned and played five games. He was then sidelined because the team said he was suffering from a virus. Eighteen days later, however, they said he had concussion-like symptoms.

The Eastern Conference-leading Flyers have three players - Pronger, Brayden Schenn and Claude Giroux - who could have concussions. Giroux was hit in the back of his head in a collision with teammate Wayne Simmonds on Saturday, and the Flyers said he will miss Tuesday's game in Washington. They have not given specifics of his injury.

Schenn is sidelined indefinitely with what the club has called a "mild concussion."

Douglas Smith, director of the center for brain injury and repair at the University of Pennsylvania, said there is "no such thing" as a mild or minor concussion. He said any kind of concussion often leads to chronic headaches.

How long should a player sit out after suffering a concussion?

"I would have to sit 50 years before I went back in," he said.

Once a person has suffered a concussion, "we suspect you have a lower threshold to have an exaggerated response to another smaller hit," Smith said. "Maybe a tiny hit will be devastating because the brain has a much lower tolerance to the next hit."

The Flyers do not allow reporters to speak to trainer Jim McCrossin on any medical matters, including recovery from concussions.

When it was announced Pronger had a "virus" last month, general manager Paul Holmgren said it was not connected to the eye injury.

The veteran defenseman passed a concussion test, but the headaches continued. (In an unrelated matter, Pronger had arthroscopic surgery on his left knee on Dec. 2.)

Since Pronger now has concussion-like symptoms, there has been speculation that it is related to when he was hit in the eye in late October.

Smith, who has spent the last 18 years devoted to neurotrauma research, said a blow to the eye "certainly can cause rapid acceleration of the brain, which can cause a concussion."

The Flyers announced that Pronger had a "virus" and headaches on Nov. 21, which was nearly a month after he suffered the eye injury.

With most concussions, the headaches start "within days or a week," Smith said, but it can be longer.

During the five games he played after returning from his eye injury, Pronger said he does not remember getting hit in the head during that time.

But Smith said that "any kind of hit" to another part of the body could have triggered the problem, since the head may have already been injured.

"Another hit can send spasms," he said.

Smith said 15 percent of people who suffer a "mild" concussion "go on to have a persistent cognitive dysfunction and their processing speed is lower and their memory is not as sharp for a long time, perhaps for the rest of their life.

"On top of that, this is an injury that is known for increasing the chances of Alzheimer's disease. This is an injury that can keep on taking."

When a player is cleared to play, "it just means he's passing certain tests, but it may be setting him up for a big fall," Smith said. "If you have another hit . . . it could lead to more damage."

Because teams have millions of dollars invested in players, most players try to come back from concussions.

"But do you want to become less of who you are?" Smith asked. "At what point do you say, 'I kind of like who I am?' What you have in your brain is pretty precious. You don't have a spare - and you don't want to spend the rest of your life down a quart."

Smith said hockey helmets don't have nearly the same protection as football helmets because of their design and that there is "not enough padding compared with football."

Recently a group of former athletes - including ex-Flyer Keith Primeau - physicians and researchers teamed up in an attempt to reduce concussions.

Primeau was forced to retire in 2006 after suffering his fourth concussion, and he still feels the effects today. In an effort to avoid this happening to other athletes, Primeau is promoting the newly launched Impact Indicator.

Produced by a sports safety company, the device is a helmet chin strap that uses sophisticated technology and software with a built in "indicator" light that alerts coaches and trainers when an athlete suffers a significant blow to the head. If it meets a certain Head Injury Criteria (HIC) level, a tiny light turns red.

Some youth hockey teams have started wearing the "indicator."