A Clear Image Appears

The very simplified structure of the human eye looks like this:

If you now wonder how our eyes create images and allow us to see, then have a look at the tip with the pinhole camera. Unlike many animals, the human eye has a lens in addition to the aperture. This lens is located behind the aperture, which is made of the pupil and the iris. Our lens makes sure that more light can enter our eyes and it also creates a clear image on the retina. In order for us to focus on both; close by and distant objects, our eyes developed a strategy. When we use a magnifying glass we simply vary the distances to find the perfect focal distance. This is impossible for our eyes. Our eyes' strategy is quite different; our lens is elastic and changes its shape with the help of a circular muscle called the sphincter. This muscle is able to stretch the lens to that it flattens. If the muscle is relaxed, the lens is strongly rounded. This changes the focal distance of our lens. This adjustment of the focal distance is called accommodation. Only because of accommodation we can have clear images of both close by and far away objects on our retinas.