Our eyes have what is called a "dark focus."

Our eyes have what is called a "dark focus." This is the point in space where your focus would be if your eyes were totally relaxed. Imagine yourself in a pitch black room. In such an environment, where you can't see anything, your eyes are actually focusing on a fixed point in space, hence "dark focus." This focus, also known as the resting point of accommodation (RPA) is unique to every individual, though it usually rests more than three feet away from your face, and does not depend on time of day or age. When you look at something, your eyes exert effort in moving their focus away from the RPA and towards the object that you are looking at. The difference between your RPA and what you're focusing on is known as the lag of accommodation. Now imagine what would happen if your eyes began to play a tug-of-war with your focus. This is exactly what your monitor causes your eyes to do. The pixels generated on your screen are known as Gaussian images because they exhibit a Gaussian curve or distribution. That is, they are brightest, and have the clearest definition at their centers, while their edges fade and are less distinct.