Researchers have recently discovered yet another scary side effect of blows to the head: impaired eye function.

Repeated hits, even sub-concussive ones, can lead to issues with the eyes’ ability to focus, a new study reveals. Although it’s unclear whether the effects could be long-term – more research is needed, though the issues seem to heal naturally about three weeks postseason – this new development could be a valuable diagnostic tool. Even smaller impacts that don’t lead to concussions can now be evaluated and measured for their severity.

In the five practices studied, 1,200 sub-concussive hits were recorded to the 29 football players’ heads, and those who were hit more than 40 times gradually had more and more trouble with their eyes’ ability to focus without double vision. In the future, if players are tested for similar effects at regular points during the season, the ones who are suffering from the repeated blows could be given proper treatment, even if no concussion is diagnosed.

*Scientists have no conclusive evidence as to whether or how the reduction of g-forces during impacts reduces the number or degree of concussions and head injuries. GelDefender products provide supplemental padding as well as cooling and comfort benefits when used with helmets and caps. Participants in activities in which head impacts can occur should always use tested and approved helmets for protection. However, no helmet or supplemental padding can protect the user from all serious head or neck injuries that can result from impacts.