What is the basis on which an astronaut is recruited to go in space?

In order to become Astronaut, you require to have min 1000 hour of flying experience and degrees in the field of Science and Engineering. India's first two Astronauts were from Fighter flying branch of Indian Air Force and were trained in Russia then USSR on Government of India expenses. NASA advert

Ability to pass the NASA long-duration Astronaut physical, which includes the following specific requirements Distant and near visual acuity must be correctable to 20/20, each eye. Good luck.