Editing Cornea (section)

==Function==
===Refraction===
The optical component is concerned with producing a reduced inverted image on the retina. The eye's optical system consists of not only two but four surfaces—two on the cornea, two on the lens. Rays are refracted toward the midline. Distant rays, due to their parallel nature, converge to a point on the retina. The cornea admits light at the greatest angle. The aqueous and vitreous humors both have a refractive index of 1.336-1.339, whereas the cornea has a refractive index of 1.376. Because the change in refractive index between cornea and aqueous humor is relatively small compared to the change at the air–cornea interface, it has a negligible refractive effect, typically -6 dioptres.<ref name="ReferenceA"/> The cornea is considered to be a [[Lens (optics)|positive meniscus lens]].<ref>{{cite book|author1-link=Irving P. Herman|last1=Herman|first1=Irving P.|title=Physics of the human body with 135 tables|date=2007|publisher=Springer|location=Berlin|isbn=978-3540296041|page=642}}</ref> Some species of birds and chameleons, and one kinown species of fish, also have corneas which can focus.<ref name="SchwabDubielzig2012">{{cite book|author1=Ivan R. Schwab|author2=Richard R. Dubielzig|author3=Charles Schobert|title=Evolution's Witness: How Eyes Evolved|url=https://books.google.com/books?id=ebfVi5ASD0AC&pg=PA106|date=5 January 2012|publisher=OUP USA|isbn=978-0-19-536974-8|page=106}}</ref>

===Transparency===
[[File:-66wiki.jpg|thumb|The cornea becomes opaque after death{{br|}}(provenance: genus ''[[Bos]]'')]]
Upon death or removal of an eye the cornea absorbs the aqueous humor, thickens, and becomes hazy. Transparency can be restored by putting it in a warm, well-ventilated chamber at 31&nbsp;°C (88&nbsp;°F, the normal temperature), allowing the fluid to leave the cornea and become transparent. The cornea takes in fluid from the aqueous humor and the small blood vessels of the limbus, but a pump ejects the fluid immediately upon entry. When energy is deficient the pump may fail, or function too slowly to compensate, leading to swelling. This arises at death, but a dead eye can be placed in a warm chamber with a reservoir of sugar and glycogen that generally keeps the cornea transparent for at least 24 hours.<ref name="ReferenceA" />

The endothelium controls this pumping action, and as discussed above, damage thereof is more serious, and is a cause of opaqueness and swelling. When damage to the cornea occurs, such as in a viral infection, the collagen used to repair the process is not regularly arranged, leading to an opaque patch (leukoma).