pigmented colorants: dependence on media and time - Cornell ...

protectively tucked away in the eye socket. The basic layout of the eye is three
concentric layers, two fluid-filled interior chambers, and the devices for capturing
light at the front of the eye. The outer two layers protect and nourish the eyeball
(fibrous and vascular tunics, respectively), while the retina (the innermost layer)
initiates the neural messages bound for the brain. What we see as the white
portion of one’s eyes is the sclera, which is part of the outermost, fibrous coat.
It’s tightly packed fibers give the sclera is toughness, protecting and holding the
pressure-filled shape together. At the very front of the eye, the outer coat loses
its coloring and becomes transparent. The surface bulges into a slight hemisphere,
and is called the cornea. The cornea’s transparency is critical for vision, as light
must enter the eye unimpeded. This is possible because the cornea has a very
orderly arrangement of fiber and no internal blood supply of its own. Thus, it
must draw nourishment from the clear fluid in the anterior chamber. The cornea
is very sensitive to touch and any foreign bodies coming into contact produces a
number of protective mechanisms (including tears and lid-closure) to maintain its
transparency.
Figure 3.10: Cross section of the human eye, showing major layers and
structures. View is from above the left eye. Adapted from [SB02].
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