How to prevent shortsightedness?

As of now, my optician says I have 20/20 vision, also known as "Pilot Vision". Which is great, as that's the best there's.

I'm a graphic designer, so I often spend most of my working days looking at my computer, iPad or iPhone.

Will this effect the quality of my eyesight? If so, how can I prevent this?

Take a couple of minute breaks from the computer every 15 minutes to 30 minutes to give your eyes a rest. Talk to the eye doctor about any other suggestions.

NO, it's determined by your gene!

Nothing you do causes nearsightedness. There are a lot of myths, but it purely controlled by genetics.

If you are 20, you will not become nearsighted.

Basically, the focal distance of the natural lens of your eye is determined by its shape, which is determined by genetics, and the lens is fully formed and shaped by the time you are three years old. Hopefully, the focal distance of the lens matches the actual distance from the lens to the retina in the back of the eye. As your eye grows bigger, this distance increases. Children generally start out farsighted because their eyeballs are small, but their lenses are adult-sized. As their eyes grow, they become normal sighted, hopefully. Depending on the genetics of your lens and eyeball size, you can end up still farsighted or you can end up nearsighted. This growth happens between the ages of 11 and 20, and it is purely controlled by genetics.

If you are 16 and you are not nearsighted yet, you most likely never will be. If you are 20 and not nearsighted, you never will be.

Again, it's all controlled by genetics. Nothing you do will make you nearsighted or stop you from becoming nearsighted.

To be honest there's nothing you can do
You eyes are fine
Your eyes will deteriorate with age and may need glasses when older, but that's normal
If you are worried about your eyes tho, takes breaks every now and again and buy a screen protector for your computers