Editing Cornea (section)

===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>