Energy can be transferred as both a particle and a wave.
4. Ways of Sensing
4.1. Near and Far Sightedness
The lens of the eye is flexible and soft. The muscles attached to it can change the shape of the lens to make it thinner for seeing things far away, or thicker for close-up viewing. Unfortunately some people have an eyeball that is too long or a cornea or lens that is too convex. Either way, they are able to see things up close without problem, but they can’t see things at a distance because the image forms in front of the retina and is blurry.
Because the person can see near objects, this condition is called nearsightedness, or myopia. Since nearsighted eyeballs focus too much, a lens that diverges light can improve vision. A concave lens causes the light rays to spread apart before they reach the lens in the eye, which forces the image back onto the retina so the person can see clearly.
In this condition, the eyeball is too short or the cornea and lens are not convex enough. Farsighted people can see distant objects but are unable to focus on close-up objects. Because they can see things at a distance, this condition is called farsightedness, or hyperopia. Images are formed behind the retina, not on it, and this causes close-up images to be blurry.
Since the light rays do not converge enough, a lens is needed to correct that. Convex lenses help hyperopic eyes to see clearly by moving the image forward from behind the retina to focus on the retina