Good vision is the result of a proper focusing of sharp images onto the retina of the eye.
In general, this is the point of sharpest focus. Eyes with normal vision see images at a close distance as well as images at a far distance clearly. The focal point is located exactly on the retina. If the focal point is not located exactly on the retina but rather in front of or behind it, blurry images are produced. This is referred to as a refractive error or vision disorder, or it is also more commonly called bad vision.