'Miss! Are your classes making me blind?'

"Miss, miss! Are your classes making me blind?"

It sounds like a ridiculous question, but it may actually be grounded in science.

A new study, published in the British Medical Journal, says there's "strong evidence" that the longer we spend in education the more likely we are to need glasses.

So as concerned hands shoot up in the classroom, how could teachers cope with a barrage of questions?

"Miss, this is old news, we already know this!"

Well kind of, this idea's been around for donkey's years.

But nobody has been able to "prove" that being in the classroom is damaging our eyes.

"But why, Miss?"

Because it's not ethical to experiment on kids by locking you up for decades and seeing how it affects your eyes. Unless you're volunteering?

"No way Miss, but they know now?"

Scientists at the University of Bristol and the University of Cardiff used a very clever trick to work it out.

They looked at 68,000 people and their DNA.

"What's DNA?"

It's like an instruction manual for building people and we all have one that's unique to us.

Some people have instructions that affect the way their eyes grow and are more likely to become short-sighted.

DNA is really powerful stuff. There are even bits of DNA that can predict how long you will stay in education.

"So what?"

The study showed kids that had instructions that made them short-sighted didn't spend longer in school.

But those with instructions linked to loving the school and university were more likely to be short-sighted.

It suggests that something about the classroom is damaging our eyes.

"That's pretty hardcore science."

Yes it is. And if you want to be really clever then you can use the proper name for being short-sighted - myopia.

"How bad are my eyes going to get, Miss?"

It's impossible to say, everyone will be affected differently.

But on average, the difference between dropping out at 16 and staying on until the end of university is "minus one dioptre".

"Huh?"

Opticians measure the ability of your eye to focus light in dioptres.

Minus one dioptre is relatively mild, but it's enough to need glasses for driving.

"But my chunky frames are so totally in right now, what's the fuss?"

I like your glasses too, but severe myopia can cause problems.

It increases the risk of having retinal detachment or myopic maculopathy and both can make you blind.

"Sounds grim, Miss."

That's not the half of it. When you're young your eyes start off long-sighted and as you grow, your eyes change and your vision corrects itself.

So if you become short-sighted really young then things are only going to get worse.

"So I should drop out of school?"

Errrm, no.

One of the researchers, Dr Denize Atan, said: "Obviously we do want people to go to school, but we want to stimulate discussion about how we teach our children."

"Miss, I'm looking on Instagram and loads of kids in China have glasses."

Hand your phone over, you can have it back at the end of the day.

But, you're right, in some parts of China around 80% of school-leavers have myopia.

"Miss, my mum says if I keep staring at my phone then I'll go blind."

Well this study was on people who started school more than 50 years ago.

"So they're really old now, Miss?"

I'm ignoring that.

But it means we don't know how modern life is affecting how our eyes develop and Dr Atan says "we could be brewing something in the future" because of the amount of time we're all spending indoors.

"I'm bored now, can I play outside now?"

You can wait until dinner time, but spending time outside seems to protect the eye.

There's lots of studies in South East Asia at the moment and some suggest bright light helps the eye develop normally and prevent myopia.

"Miss..."

Enough! I've got a spelling test for you.

Follow James on Twitter.

Conflict of interest: I love my glasses.