eye histo+ ana

• The eyeball has three thin tunics

  (1) an external fibrous tunic that gives form to and protects the eyeball—it is the only complete tunic;

  (2) a middle vascular tunic that consists largely of blood vessels and smooth muscle and is concerned with the nutrition of the eyeball and the regulation of the shape of the lens and size of the pupil; and (3) an internal nervous tunic that consists largely of nervous tissue and is the layer most directly concerned with vision, that is, the translation of visual stimuli into nerve impulses for interpretation by the brain.
• The eye of mammals is a sensory organ designed for vision.
• The fibrous tunic of the eyeball - made up of very dense collagenous tissue, which by resisting the internal pressure, gives the eye shape and stiffness.

  consists of the sclera and cornea, which meet at the limbus
• sclera is the opaque posterior part of the fibrous tunic “the white of the eye"

  cornea forms about one quarter of the fibrous tunic and bulges forward It is composed of a special kind of dense connective tissue arranged in lamellar form
• The cornea does not contain blood vessels nutrients for its cells permeate the substantia propria from vessels in the limbus or are carried to its surfaces in the lacrimal fluid and aqueous humor
• The vascular tunic of the eye (also known as the uvea) lies deep to the sclera

  It consists of three zones: choroid, ciliary body, and iris,
• The choroid contains a dense network of blood vessels embedded in heavily pigmented connective tissue
• dorsal part of the fundus the choroid forms a variously colored, light-reflecting area known as the tapetum lucidum This is an avascular layer (cellular in carnivores, fibrous in ruminants and horses)
• The third and smallest part of the vascular tunic is the iriswhich is suspended between the cornea and lens
• The iris consists of three layers: an anterior epithelial layer continues across the iridocorneal angle and blends with the posterior epithelium of the cornea, a middle layer of connective tissue stroma contains the two smooth muscles, and the posterior layer of pigmented epithelium is the forward extension of the pigmented layer of the retina
• The color of the iris determines the “color of the eye” and depends on the number of pigmented cells present in its stroma and on the type of pigment in the cells.
• Ventral to the posterior pole it presents a small cribriform area through which pass the fibers of the optic nerve
• The eye contains three fluid-filled regions,
• ten layer of photosensitive layer of retina are

  Pigment epithelium

  Layer of rods and cones

  Outer limiting membrane (usually not apparent)

  Outer nuclear layer

  Outer plexiform layer

  Inner nuclear layer

  Inner plexiform layer

  Ganglion cell layer-nerve cell

  Nerve fiber layer

  Inner limiting membrane
• the optic disc, is a blind spot. In contrast, an area of maximum optical resolution (macula) is located a short distance dorsolateral to the optic disc.
• mydriasis (enlarged pupil)
• The transparent, biconvex lens is avascular. It is composed entirely of epithelial cells enclosed within a homogeneous capsule
• The cells on the anterior surface of the lens just below the capsule are simple cuboidal and form the lens epithelium
• The sclera consists of densely interwoven bundles of collagenous fibers arranged parallel to the surface of the wall of the eye.

  also fibroblasts, some fine elastic fibers, and scattered melanocytes, especially in the innermost region of the sclera.