What you are actually seeing immediately is the lack of circulating blood to the sclera (the white part of the eye) shortly after death. Because we have numerous vessels in the sclera that, even when you're eyes aren't bloodshot, lend to the normal, living appearance of the eyeball, death produces a distinctive and unforgettable change to this as the circulation stops.
The true "clouding over" of the cornea doesn't occur until somewhat later on and is a result of the subsequent lack of flow of the aqueous humor underneath the cornea. This space is called the anterior chamber of the eye. Basically, the cornea is just a tough, clear, three-layered membrane of tissue, the surface of which is supplied with oxygen mainly by air and, more importantly, the undersurface of your upper eyelid (i.e., when you blink and shut your eyes for extended periods). However, the aqueous humor underneath flows constantly while alive produced from the ciliary body exiting back through the canals of Schlemm which supplies oxygen and nutrients the inner layer of cells in the cornea. Over production of aqeuous humor results in the so-called "chronic open angle" glaucoma syndrome, and a blockage of the canal of Schlemm results in "acute closed angle" glaucoma, the latter of which is a medical emergency. The middle layer of the cornea is very carefully layered extracellular collagen that doesn't actually require oxygen.
When the circulation stops at death, you eventually see a "fogging over" of the cornea as a result of the stagnation of this fluid and subsquent death of the inner layer of cells.
That's basically it. Hope that explanation helped.
-TT
