The image formed on the retina is a result of the light bending activity of the lens, which is a real image. The real image is reversed from left to right, upside down, and smaller than the object really is. Vision problems occur when a lens is to strong or too weak or from structural problems of the eyeball.
When a person looks at an object it is either giving off light or light waves are reflecting off of it. When light waves enter the eye, the object is focused on the retina causing the waves to bend. The convex area of the cornea refracts the light waves from the object.
