How can the visual deficiencies known as myopia and hypermetropia be optically explained?
Myopia is the visual condition in which the images are produced before (in front of) the retina. Hypermetropia is the visual condition in which the point of image formation is beyond (behind) the retina. Actually myopia is due to an enhance in the distance among the retina and the crystalline lens, mainly caused by a slight flattening of the eyeball. In hypermetropia the retina is too close to the crystalline lens because of slight shortening of the eyeball.