Sorry firstborns, you might be smarter but apparently you're also more likely to have these health conditions.

Image: No wonder little sister Dannii looks so pleased (Getty).

It’s said birth order can influence everything from a child’s personality to their future professional success, and firstborns seem to get all the big wins. To begin with, they’re apparently more ambitious and perform better academically. (Hmph. Show-offs.)

Now, however, a new study has revealed some unlucky news for eldest children: they’re more likely to be short-sighted than their younger siblings.

Researchers at the University of Cardiff have explored the relationship between myopia — AKA short-sightedness or near-sightedness — and birth order, finding the condition is 10 per cent more common in first born children.

The study, published in the Journal of the American Medical Association, also established eldest children are 20 per cent more likely to develop a severe form of myopia, which can lead to holes and tears in the retina and retinal detachment, making early diagnosis essential to future eye health. Ouch.

It seems parents, and the 'educational exposure' they provide to their first child, has something to do with this.

Study author Jeremy Guggenheim speculates that as parents often devote a higher level of time to their firstborn's educational development, this educational exposure may lead to them spending less time outdoors.

"Our evidence... supports the idea that reduced parental investment in children's education for offspring of later birth order contributed to the observed birth order vs myopia association," he said.

Spending time outdoors and away from electronic devices is critical to early prevention, and Professor Kovin Naidoo of the Brien Holden Vision Institute has said both teachers and parents should both play a part in screening children that are at risk of vision impairment. (Post continues after gallery.)

"Parents should encourage their children to spend time outdoors for at least two hours each day. They should also ensure children don't spend too much time on electronic devices, such as tablets, mobile phones, electronic games, television and other activities which requires them to focus close up for long periods."

While this study examined a group of 15 to 22 year-old subjects from the United Kingdom and Israel, the prevalence of myopia continues to rise across the world, with the condition currently affecting 1.45 billion people worldwide. It's been predicted that by 2050, almost five billion people will be affected, with many significantly at risk of becoming vision impaired.

Unfortunately, the condition is not curable or reversible, although behavioural and optical intervention can help slow its development and decrease the chances of sufferers developing high myopia.

Sorry firstborns: you don't win this round. And that noise you hear right now? It's the younger siblings of the world high-fiving one another.

Are you a firstborn? Do you buy into any of the 'birth order' speculation?