By Stephen Matthews Health Editor For Mailonline
Published: 18:18 GMT, 13 February 2020 | Updated: 18:29 GMT, 13 February 2020
Heading a football can trigger instant brain changes that affect vision, researchers have warned.
A study of dozens of football players found headers cause short-term damage to the circuit linking grey matter with the eyes.
The findings add to mounting evidence blows to the skull during football games can be harmful even if they don't cause concussions.
It comes as the Football Association is set to limit how often young players can head balls in training to address growing health fears.
A study of dozens of football players found headers cause short-term damage to the circuit linking grey matter with the eyes
Indiana University researchers conducted the first trial of its kind, which studied 78 football players.
Around half of them were asked to perform ten headers. The other volunteers were only allowed to kick the ball.
The study, published in JAMA Ophthalmology, found heading impaired brain wiring that links eye and cognitive functions.
These changes were measured with tests of eye movement and mental abilities such as attention, language and concentration.
Lead researcher Dr Keisuke Kawata said: 'The findings suggest sub-concussive head impacts may affect neuro-eye function, at least in the short term.'
The control group performed better on the vision tests than the players who were told to head the football.
Although the system is sensitive to brain trauma the effect of sub-concussive head impacts has remained unclear, he said.
The volunteers executed the headers with footballs projected at a speed of 25mph (40kmph) to mimic typical events during matches.
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All the volunteers in the control group followed the same protocol but with 10 kicks – instead of headers.
Dr Kawata suggested the findings would apply to other contact sports, which may include boxing, American football and rugby.