This exhibit consists of four model eyeballs that are about 10 times human size. The models represent a nearsighted eye, a farsighted eye, an eye with an adjustable focal length, and an astigmatic eye. All but the adjustable eye are provided with external corrective lenses that can be added or removed by the visitor. There are nearby and distant objects for the eyes to focus on. Real images are formed on the back of each model, revealing the image inversion which takes place in the eye as well as the corrective effect of lenses.