Why do screens affect your eyes ?

Question: Why do screens affect your eyes ?
- Keywords:
  organ,
  technology,
  vision
Asked by to Andrei, Ekbal, Gemma, Helen, Ruth on 18 Jun 2014. This question was also asked by .
- Ruth Nottingham answered on 18 Jun 2014:
  
  Hi
  
  Looking at a screen for a long time can strain your eyes, because you eyes are focusing on just one distance. You can avoid this by taking breaks from looking at a screen to look at things that are further away as this relaxes the focusing muscle inside the eye. Eye strain is not a serious problem, it can give you headaches or tired eyes but these symptoms will go away once you rest your eyes.

Question: Why do screens affect your eyes ?