Long focusing of the eyesight on the objects that are close to you and that are of small size (e.g. screens of mobile devices with insufficient contrast) leads to the strain of eye muscles. As it is known, the human eye is arranged so that the relaxation of the eye muscles is possible only when we look into the distance. This happens not so often, however, in the «urban jungle» and when we operate the computer all day long. It is particularly damaging for children and adolescents to stare at screens of communicators and handheld game consoles. In short (though sometimes we do not want to acknowledge this) we need to know when to stop...