A British astronaut is being sent into space to investigate why space travel leads to short-sightedness.

European Space Agency astronaut Tim Peake will spend six months on the International Space Station (ISS) from November 2015 as part of a research project launched by scientists into why people who spend extended periods in space return with permanently deformed eyes.

Researchers believe that exposure to a weightless environment for a long period of time changes the shape of astronauts' eyeballs, which affects their vision.

It was expected that the problem would rectify itself once astronauts returned to Earth, but studies have shown that this does not happen, with some being left with permanent damage.

A research paper recently published by Nasa found that more than 30% of astronauts who had visited the ISS experienced problems with their sight.

Scientists at Nasa's Johnson Space Center studied astronauts suffering microgravity ocular syndrome and found that vision changes are common in astronauts and are associated with the optic nerve sheath thickening and optic disc oedema.

"This shift in vision is one of the highest research priorities," Peake told The Sunday Times. "Some astronauts returned with changes in near and mid-vision.

"It's thought that increases in intracranial pressure [the pressure of fluids inside the skulls] is flattening the back of the retina.

"The retina is then remembering that shape and in some people, it is not adapting back to its original shape, leaving them with a permanent shift in vision, including becoming short-sighted."

Astronauts also suffer from a number of health issues beyond poor vision. In zero gravity, bodily fluids shift from the legs to the heart and head.The brain then reduces body fluid because not much is needed, and the heart shrinks because pumping blood in zero gravity is very easy.