The crystalline, also known by the name of “slow”, is in all respects a magnifying glass (of about 11mm in diameter for 4.5 mm thick) that, positioned behind the "Iris" made from 'iris and allows the focus of the objects on the retina varying its accommodative power. The lens is surrounded by a "bag" said capsule (where today is located the artificial lens) and is suspended behind the iris, by a system of small fibers (la zonula) that anchor to the ciliary body. You can imagine how a balloon full of water linked by wires to the equator. The laxity or tension exerted by these wires would vary the thickness of the balloon from globose to flat. In the eye the lens works just as well. In a normal eye (emmetropic), that is free from defects of refraction, together allows the lens to the cornea, parallel light rays that come from infinity, to achieve sharp focus on macula thereby generating clear images on the retina. In the near vision (in which therefore the rays which penetrate into the eye are not parallel, but divergent), the lens can change its thickness compensating in this way for the blur close (process called accommodation ). In fact always in an emmetropic eye (but the same problem occurs also in all refractive errors), tale meccanismo, efficient at a young age exceeded 45 age, gradually loses its efficiency resulting in a blurring of images to close so that these, to be able to be re-focused, need correction with glasses. This loss of efficiency is commonly defined (Presbyopia). With advancing age, addition to the increased inability of reward, the lens loses its main feature, transparency, starting to become opaque in a slow, gradual and subjective to determine until a serious obstacle to the vision. The lens is defined as generically “cataract” (cortical and nuclear) and the only way to remove this is the clouding of vision 'cataract surgery with implantation of artificial lens (IOL).