The eye is one of the most important and complex structures of the human body through
which we see, perceive (about 80% of learning comes through the eyes), and then react
to this physical world. It is the second most complex structure of the human body, in
context of its working and signal transmission after brain. The human eye consists of
three layers, enclosing numerous anatomical structures (Fig. 2.1a). The fibrous tunic is
the outer layer which is comprised of sclera (white portion) and cornea of the eye. The
vascular tunic or uvea is the middle layer which is formed by the choroid (the posterior
part), ciliary body, iris, and pigmented epithelial layer. The innermost light sensitive
layer is called retina, which has a rich blood supply anteriorly by choroidal and
posteriorly by retinal blood vessels (O'Neill et al., 1998).