I am sorry but your father is very uneducated...
That is a complete
myth. You can safely leave your computer open day and nights and live in the same room with the computer your whole life, and nothing will happen to you.
The only thing that can hurt you by using a computer, is listening loud music with the headphones for long times and regularly, which can hurt your ears. Your eyes also may be irritated if you look at the monitor daily and regularly and feel itchy, but it will never affect your eyesight, that is a complete
myth as well.
( I am not a physicist or a doctor, but even the youngest children can know that parents create things like this to get them away from computers and televisions, so they can read a book and study for their schools.)