ANATOMICAL STRUCTURE OF EYE
The eye is a special sense organ made up of three coats, or tunics, as follows:
1. The outer fibrous layer of connective tissue forms the cornea and sclera.
2. The middle vascular layer is composed of the iris, ciliary body, and choroid.
3. The inner neural layer is the retina.Within this globe are three spaces: the anterior chamber, posterior chamber, and vitreous chamber. The crystalline lens is located in the region of the posterior chamber.
The outer dense connective tissue of the eye provides protection for the structures within and maintains the shape of the globe, providing resistance to the pressure of the fluids inside.
The sclera is the opaque white of the eye and is covered by the transparent conjunctiva.
The transparent cornea allows light rays to enter the globe and, by refraction, helps bring these light rays into focus on the retina. The region in which the transi-tion from cornea to sclera and conjunctiva occurs is the limbus.
The vascular layer of the eye is the uvea, which is made up of three structures, each having a separate function but all are interconnected. Some of the histologic layers are continuous throughout all three structures and are derived from the same embryonic germ cell layer. The iris is the most anterior structure, acting as a diaphragm to regulate the amount of light entering the pupil.
The two iris muscles control the shape and diameter of the pupil and are supplied by the autonomic nervous sys-tem. Continuous with the iris at its root is the ciliary body, which produces the components of the aqueous humor and contains the muscle that controls the shape of the lens.
The posterior part of the uvea, the choroid,is an anastomosing network of blood vessels with a dense capillary network; it surrounds the retina and suplies nutrients to the outer retinal layers.
The neural tissue of the retina, by complex biochem-ical processes, changes light energy into a signal that can be transmitted along a neural pathway. The signal passes through the retina, exits the eye through the optic nerve, and is transmitted to various parts of the brain for processing.
The interior of the eye is made up of three chambers. The anterior chamber is bounded in front by the cornea and posteriorly by the iris and anterior surface of the lens. The posterior chamber lies behind the iris and surrounds the equator of the lens, separating it from the ciliary body.
The anterior and posterior chambers are continuous with one another through the pupil, and both contain aqueous humor that is produced by the ciliary body. The aqueous humor provides nourishment for the surrounding structures, particularly the cornea and lens.
The vitreous chamber,which is the largest space, lies adjacent to the inner retinal layer and is bounded in front by the lens. This chamber contains a gel-like substance, the vitreous humor.
The crystalline lens is located in the area of the posterior chamber and provides additional refractive power for accurately focusing images onto the retina. The lens must change shape to view an object that is close to the eye, through the mechanism of accommodation.
OPTOMETRY-SHARP VISION
Optometrist