Repetitive Football Hits May Cause Visual Abnormalities

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Repeated sub-concussive hits appear to cause short-term visual changes, a new study shows. Erich Schlegel-USA TODAY Sports via REUTERS

It's clear that football has a problem with concussions and brain injury. But more and more work hints that repetitive hits to the head, even those that don't cause concussions, can lead to problems down the road. Now, new research suggests that repetitive "sub-concussive" hit (i.e., those that do not cause concussion) may impair vision.

In a study published May 12 in the journal JAMA Ophthalmology, researchers from Temple University and elsewhere found that college football players who took a lot of hits had a reduced ability to focus on objects close to their eyes, compared to their peers who weren't knocked around as much.

In the paper, the scientists measured the number and intensity of hits 29 college football players took over the course of five full-contact training camp practices, by placing an accelerometer in the athletes' mouth guards. They then classified players into either a high- or low-impact category. Afterward, they performed what's called the "near point of convergence" (NPC) test, which gauges a person's ability to focus on an object as it gets closer and closer to the eyes. (NPC measures the distance at which an object can no longer be focused on without double-vision, hence lower scores are better.) Those in the high-impact group had a reduced ability to focus on objects nearer to their eyes after practices—and thus a higher NPC score—compared to those who were hit less.

When on object gets too close, the eyes eventually cannot maintain "convergence" and double-vision occurs. At that point, "the muscles and nerves around the eyes are not able to maintain focus on a single object," says Temple neuroscientist and lead author Dianne Langford. To keep focus requires a careful calibration of these nerves and muscles. This finely-tuned ability gradually declines with age, and is sensitive to brain injury—previous work has shown that concussions cause a significant increase in NPC score. This is the first study to show the same can happen, though to a much smaller degree, with repetitive sub-concussive hits.

Even within the high-impact group, those who were knocked around more had a greater degree of disruption in their ability to focus at close range.

Langford says they don't know for sure what is causing the change in vision, but it could be due to injury in the brainstem resulting from the rotational torque of taking hard hits.

It's important to point out, however, that three weeks after full-contact practices ended, visual scores improved and reverted to their baseline levels, Langford says. But, she adds, she'd be concerned about somebody undergoing this level of contact for many years, or an entire career. "I'm really not sure what the outcome may be," she says. "It's like if you were to stress a muscle, when you rest, you recover. But if you continue to [take repetitive hits to the head] over and over, I don't know if there'd be a full recovery."

There are limitations to the study. It was relatively small, including only 29 players. And the changes in vision were subclinical; none of the athletes complained of any symptoms after practices, and didn't notice any changes in their vision.

"Therefore, one wonders if these changes are clinically meaningful," write physicians Andrew Lee and Steven Galetta, respectively with Houston Methodist Hospital and NYU Langone Medical Center, in a commentary published alongside the study.

Nevertheless, it adds to a body of work suggesting repetitive subconcussive hits, sustained over years, may cause brain damage. Some research has for example hinted at a link between a history of subconcussive impacts and chronic traumatic encephalopathy, a progressive degenerative disease of the brain, Langford says.

"If the findings of this study are confirmed, it will provide further impetus to limit full-contact

practices in collision sports," Galetta and Lee write.