Watch to learn how and why spectacles/contact lenses are used to correct defects of vision and how exactly they affect the human eye.
The demonstration in this video uses lasers and lenses to simulate what happens inside the human eye. You can see how an eye with myopia (shortsightedness, nearsightedness) and an eye with hypermetropia (farsightedness) is different from a normal eye. The demonstration also shows why a diverging lens is used to correct shortsightedness and why a converging lens is used to correct farsightedness.