This is a simulation of the optics of the human eye. Move the object closer to or farther from the eye (drag the object or use the Object Position slider). Use the focus slider to change the shape of the lens of the eye to adjust its focal length. When the refracted rays in the eye come together on the retina, the image is in focus. In some special cases you have the option to see how corrective eyewear can be used to overcome vision problems like nearsightedness and farsightedness. Adjust the Overlay Eye Anatomy slider to see a detailed image of the anatomy of the eye. Note: I believe this image to be in the public domain. If it is not and you own the copyright, please contact me and I will remove it right away.[br][br]Some Questions:[br][br]What is different about the rays of light that reach the eye from an object near the eye, as compared to rays that come from an object far from the eye?[br]What is nearsightedness? In nearsightedness, what is the issue with the lens? What type of lens can correct for this?[br]What is farsightedness? In farsightedness, what is the issue with the lens? What type of lens can correct for this?[br]What about a person that needs bi-focals? What is the issue with the lens? What type of lens can correct for this?[br]_the eye can see nearby objects clearly but the distant objects appear indistinct is nearsightedness[br]_Farsightedness-In this defect the human eye can see distant objects clearly but cannot see nearby[br]objects distinctly.