How does a healthy eye work?
When looking at an object in the distance a normal-sighted eye will focus the light rays entering the eye onto a pigment layer of the retina to produce a sharply focussed image. The image is sensed by a virtually uncountable number of point-form sensory cells and, just as in a camera, it is upside down and the wrong way round. Our brain processes the visual information from both eyes to produce a unified visual image, the image of what we see, and what we want to see.
Is it possible to focus sharply on both near and distant objects?
Up to the age of roughly 40 we can adjust the lens in our eyes to produce sharp images of both near and distant objects. This ability is called accommodation