The cornea is the '"goal" of the outer eye, a sort of glass dome difficult to visualize, because totally trasparente, In fact, we can only observe the curvature profile ( looking at an eye from the front we see the color of the iris, but we do not notice the cornea). The cornea is avascolare, ie without blood vessels, while being an extremely vital tissue. Finally, it is Mirror ie its curvature is extremely smooth and with the tear film that bathes, has the characteristic to reflect and refract the images. These characteristics, unique in the entire human body, allow it to send the light rays within the eye with a proper curvature, atta (along with that offered by the crystalline) to convey to the sharp images on the retina (in particular on fovea ). Depend on this specialized tissue, with a central thickness of only 0,54 mm, on which we apply contact lenses, i 2/3 of optical power Eye. The anterior corneal curvature is 48.6 diopters (D) and the rear average is -6.8 D (with a total refractive power of the cornea of about 43 diopters(D)). With age, the corneal curvature changes slightly. In principle, in a normal subject the adult cornea is more curved on the vertical meridian (of approximately 0.5 D) with respect to the horizontal meridian, condition responsible for astigmatism said "Physiological second rule". This difference between vertical and horizontal curvature decreases with age, to zero around 70 age (tendency to evolve towards astigmatism against the rule in old age). In the anatomical structure of the cornea, can be recognized from outside to inside; the’ corneal epithelium stratified, the thin basal lamina of this lamina di Bowman, it stroma consists mainly of collagen fibers and which represents the 4/5 of its thickness, la membrana in Descemet and a single layer of highly specialized cells responsible for the nutrition and osmotic barrier which lines the posterior surface of the cornea which is the’corneal endothelium rear. Theendotelio è quindi lo strato più interno della cornea ed è composto da un unico strato cellulare di cellule piatte e poligonali di circa 5 micron di spessore che non hanno capacità rigenerative, la cui densità media in individui adulti è in media 2700 cell/mm2, con un range di 1600-3200 cell/mm2 ed il cui numero si riduce con l’età L’endotelio svolge un ruolo importante nel mantenimento della fisiologica sopravvivenza e trasparenza della cornea. Infatti è attraverso di esso che passano l’ossigeno dalla camera anteriore ed i nutrienti essenziali (for example, glucose, amino acids) of the cornea, mentre la trasparenza corneale viene mantenuta grazie all’azione dell’endotelio che agisce come una barriera selettiva alla penetrazione di sale e metaboliti nello stroma e pompando attivamente ioni bicarbonato dallo stroma all’acqueo evitando che la cornea si imbibisca di acqua. The cornea may be involved in inflammatory processes or infectious (keratitis) representing, if not treated promptly and radically, serious problems for visual clarity, as corneal scarring (leucomi) result in a loss of transparency with possible serious effects on vision. And 'thanks to the possibility to modify the curvature of the corneal surface, and then, ultimately the dioptric power of the entire eye, offered today by the new laser that rely most of the techniques refractive surgery.