In good news for parents concerned a Tik-Tok addiction is ruining their child's eyesight, researchers say mobile phone use does not contribute to short-sightedness.

The bad news is the myopia epidemic gripping the world is mainly caused by computer screens.

People who used a computer for six or more hours per day experienced faster deterioration in short-sightedness compared to those with low computer use, a study from The University of Western Australia found.

Samantha Sze-Yee Lee, a senior research fellow from the Lions Eye Institute, said time spent on mobile phones or tablets had no effect.

"The reason for this difference may be due to a phenomenon called 'peripheral de-focus'," Dr Lee said.

"When you look at your mobile phone, everywhere in our peripheral vision, with the exception of the small phone screen, is further away and relatively blurred. The brain registers things are generally far away and there is no need for the eye to become more short-sighted.

"When you focus on a large screen such as a desktop computer, more of our peripheral vision is taken by the screen. The brain sees that more short-distance work is involved, triggering the eyes to become more short-sighted."

Dr Lee's findings are derived from data collected from 600 young adults as part of the Perth-based Raine Study; one of the largest and longest-running studies of human health being carried out in the world.

Optometry Australia's latest Vision Index, released last year, found respondents with myopia rose three points to 40 per cent in the two years prior.

It predicted more than half of the global population will be short-sighted by 2050.

More respondents said they were concerned about their eye health since COVID, with 42 per cent saying their screen use had gone up as a result of the pandemic.

Myopia can lead to further eye conditions down the track, such as glaucoma, cataracts and retina problems, so understanding what risk factors contribute to short-sightedness is important.

"In this day and age, it is almost impossible to avoid digital screens," Dr Lee said.

"Mobile phones can easily be used outdoors, as opposed to laptop and desktop computers, and spending more time outdoors is known to be protective against myopia."

She hopes the study's findings will help scientists develop ways to manage the detrimental effect of computer use on eyesight.