We began the lesson by reviewing the definition of a lens, the effect that a lens has on light, the types of lenses, parts of a lens and lens diagram. Using pictures of the human eye, describe and explain the main anatomical parts of the eye, concentrating on the cornea and lens, which effect the diffraction of light. Explain the function of the retina in converting light energy into nerve electrical energy for transmission through the optic nerve to the optic center of the brain. Show that the image formed on the retina is inverted, but that the brain reverses it to upright. Using the diagrams of the eye, show how an image can be formed in front of the retina or behind it. Use the desktop lens kit to show how the focal point can be lengthened or shortened using the proper type of lens in front of the cornea.