Answer by  
                                                                                          quisqualis (1756)
                                                            
                          
                          
                                                          Eye strain is caused by overusing the muscles of the eyes. They become tired, and need a rest. Eye strain is often caused by doing "close work," or looking at things that are close to the eye.
  
 While resting the eyes is a good idea, avoiding eyestrain is better. Vary your visual tasks, and get glasses if you need them.