A study of 1,492 primary school children found those who spent more time looking at television or computer screens suffered narrowing of blood vessels in their eyes - a warning sign of high blood pressure and increased likelihood of heart disease.
The research, carried out by the University of Sydney asked parents to answer a questionnaire about the amount of time their children spent watching TV, playing computer games, and being physically active.
The scientists then took digital pictures of the children's blood vessels at the back of each eye. It was found children, on average, spend 1.9 hours a day watching TV or playing on computers. Those who just did this and didn't get outside for physical exercise had 'retinal arteriolar' narrowing of 2.3 microns.
However, those children who regularly got outside and spent time being active had retinal blood vessels 2.2 microns wider than the TV watching kids.