How does playing video games affect your body

By your body, you must mean as a whole. The most change will happen in your eyes. There is a muscle in your eyes called the ciliary (say: sil-ee-air-ee) muscle, it controls accommodation for viewing objects at varying distances. Which usually starts fatiguing around age 25-30, that may have increased level of fatigue due to over indulging in viewing video games in poor lighting circumstances or inadequately sized screens and may require you to get your vision corrected. From my own experience, you may have your eyes bloodshot due to staring at the screen due to excitement minimizing the amount of moisture your eye receives from blinking. If you abuse and play excessive video games you may affect your weight, especially if the video game only requires you to sit and move your fingers and wrists, not that the video games that you interact with your body will be an increase in metabolism, due to the minimal resistance it allows you to contribute, but it at least allows you to move more than just your fingers.
On a positive note, it may increase your hand eye coordination, you may also experience increased your mental reaction time, and depending on the game increase your memory or your strategy process for solving normal daily dilemmas. Phsycologically, you may experience difficulty relating to individuals without similar interests, and seclude yourself from socializing with real people by preferring only game or electronic environments. You may miss out on very important events that are fundamental for your cognitive development due to lack of human interaction, again, if you abuse the situation by committing more than average time to usage of said devices. Average usage you may need to relate to it as watching television or use your better judgment when evaluating the time you invest playing the video games.