1 List of United States cities by population. ^ 2  Population projection is that of the entity known since 2016 as Ciudad de MÃ©xico and previously as the Distrito Federal. ^  Population estimate is that of the Toronto census division, which consists solely of the City of Toronto.
Lens (optics) For other uses, see Lens. A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (elements), usually arranged along a common axis.
adjustment, especially adjustment of the eye for seeing objects at various distances. This is accomplished by the ciliary muscle, which controls the lens of the eye, allowing it to flatten or thicken as is needed for distant or near vision. Flattening and rounding of lens during accommodation.