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Study: Subtle blows to the head may harm vision

College football players who received subconcussive blows to the head had measurable changes in vision even though they reported no symptoms, a new study found.

The researchers, most of whom were from Temple University, concluded that vision might be a window into "subclinical brain damage and its recovery."

The long-term consequences of concussions as well as repeated, smaller head traumas are a hot topic among scientists. Subconcussive hits don't cause clinical concussion symptoms but may result in long-term neurological problems.

"We don't know what the effects of doing this every season for an entire career of playing football will do to your brain," said Dianne Langford, a Temple neuroscientist who was involved in the research.

Previous studies have shown that college football players endure 950 to 1,353 subconcussive hits per season.

This small study, which was published Thursday in JAMA Ophthalmology, followed 29 Temple football players during five pre-season practices. They wore mouthguards equipped with accelerometers that measured how much head impact they suffered. A total of 1,193 head impacts were recorded. The team divided the players into two groups, based on the number of hits. Twenty-two players in the higher impact group averaged 41 hits, compared to six head blows in the lower impact group.

None of the subconcussive hits was associated with changes in reported symptoms. However, the researchers did see changes when they looked at the ocular near point of convergence (NPC) in the higher-impact players.

The NPC is the nearest point you can focus on with both eyes before double vision occurs. It moved three to four centimeters farther away in players who'd taken more subconcussive hits. That is not a noticeable amount in a young man, Langford said.

The players returned to normal after three weeks of rest at the end of the season, but not during the shorter breaks between practices.

In an accompanying commentary article, Andrew G. Lee of Houston Methodist Hospital and Steven L. Galetta of New York University Langone Medical Center pointed out that the study was small and that NPC can be affected by fatigue or alcohol use. (The players had promised not to drink.)

If the findings are confirmed in a larger study, they said, "it will provide further impetus to limit full-contact practices in collision sports."

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