system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do people develop bad eyesight over the years?

Edit: I understand old age, but why do some children as small as 5 years get specs while sometimes people in their 40s dont?
gpt
If you mean why do people need reading glasses in middle age and the glasses need to get stronger and stronger as they age more then the answer is as follows ;
  
The lens in your eye gets less flexible as people grow older because layers similar to an onion build up. This lack of flexibility makes focusing on nearby objects more difficult.  
  
By shining a bright light at the writing your pupil contracts which increases the focus so you can read small writing in daylight but not indoors.