Optics
In a nearsighted eye, the cornea is too steeply curved for the length of the eye, causing light rays to focus in front of the retina. Distant objects appear blurred or fuzzy because the light rays are not in focus by the time they reach the retina. In the picture above, the arrow shows the focus of the nearsighted eye while the dotted lines represent the normal eye. The greater the myopia, the more the light rays converge and the more blurred distant objects are.

Near objects, viewed at the proper distance, can be seen clearly because the focus of their light rays matches the refractive error of the nearsighted eye. For example, a patient with -2 diopter correction is naturally in focus at 0.5 meters (18 inches). Having the focus point of the eye within arm's length is an intrinsic advantage to the myope, who always has the option of seeing well at near without optical correction. Indeed, many myopes instinctively remove their spectacles for near work, particularly after the onset of presbyopia.

Spectacle Correction
The correction of myopia with spectacle lenses accrues advantages and disadvantages for the myope. The obvious advantage is bringing distant objects into focus. The disadvantages increase in rough proportion to the strength of the lens. Most myopes begin wearing spectacles in childhood and therefore incorporate the less desirable cosmetic, convenience, and optical disadvantages into their daily routine; however, this adaption varies among individuals.

Among the optical drawbacks of minus spectacles lenses is the minification of the image. There is a 2% minification for every diopter of spectacle power. For example, a -10 diopter spectacle correction results in a 20% reduced image size. Thick lens edges and supporting frames also distort and reduce the peripheral vision.