Why is the cornea transparent?
Since it has to be transparent to allow light to enter the eye, there are no blood vessels in the cornea. It is composed of very tightly packed collagen fibers just like the sclera (i.e., the white of the eye). But whereas the collagen fibers in the sclera are randomly packed together (thus making it opaque), the fibers in the cornea are packed together in an organized pattern which is what makes it transparent. [source: http://www.peneyecare.com/theeye.
