ABSTRACT
The walls of the eye are composed of three distinct tissue layers: an outer scleral/corneal layer, that is, a collagenous layer (the anterior portion is transparent to visible light and focuses the light on the retina called the anterior sclero-corneal layer, i.e., cornea, whereas the posterior portion is opaque and called the sclera that covers approximately ve-sixth of the eye surface) that encircles the eye and provides it with mechanical strength, an intermediate vascular/choroidal layer termed the uvea, , a pigmented layer that comprises the iris (a small pigmented disk formed of muscular tissue acting as a biological aperture to control the amount of light entering the eye by controlling the size of the pupil through a combination of contraction and relaxation of radial and circular muscle bers), a ciliary body (secretes aqueous humor, which provides nutrients to the avascular tissues in the anterior segment and maintains the intraocular pressure) in the anterior portion and the vascular choroid in the posterior portion (a vast network of capillaries that supplies the retina with nutrients), and an inner retina layer (a complex enervated structure covering approximately two-third of the internal posterior surface of the globe, consisting of nervous cells connected to receptors sensitive to light, the photoreceptors, arranged on a layer of a pigmented tissue that detects and transduces light signals to the brain). The clear aqueous humor crudely resembles a ltrate of plasma (composed of brinogen, plasma bronectin, growth factors such as epidermal growth factor (EGF) and insulin-like growth factor 1 (IGF-1) and serum albumin, and novel protease, active against IGF-1 binding proteins, lower levels of urea and glucose but much higher concentrations of pyruvate, lactate, bicarbonate, and ascorbate, secreted by active processes from the ciliary epithelial cells), is lled into the anterior segment that separates the cornea from the anterior side of the lens, whereas gelatinous vitreous humor referred to as the vitreous body (a gel that is composed of water (over 98 wt%), hyaluronic acid, collagen and plasma proteins, imparts stability to the posterior components of the eye, attenuates the stresses imposed on the retina by sudden movement, and is bounded by the retina, the ciliary body, and the posterior capsule of the lens) is lled into the posterior segment. The macula lutea, a small dot, is located at the bottom of the eye, on the axis of the pupil is the highest visual accuracy zone of the eye [6-10].
