My eyes are bad, but are they getting worse?

I am a 13 year old boy and I love to play video games everyday I play about 8 hours and my eyes never hurt. I'm wearing 2 centimeter glasses and I have about 12/20. Recently, I went on vacation and since the car trip was about 13 hours until we got to destination I decided to look out the window. My dad told me looking far out was good for me. When I was in California I played about a total of 5 hours on Runescape in bad lighting. When I got home my eyes felt fine. A few days afterword I found that my eyes couldn't take that much Video Games before getting sore and tired. I'm very scared and was wondering if my eyes have deteriorated. please be honest. Are they dry, because I put on artificial tears and they don't help.