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| Human Eye Diagram with parts |
If you are looking for the detailed information about eye anatomy and physiology, you have landed at a right place. In this article, you will find the information about human eye anatomy and physiology, parts of the eye, eye diagram, human eye exam etc.
Eye is the spherical hollow organ of vision that consists of eyeball and optic nerve. The area of the eye including lids and other accessory organs of the eye; the contents of the orbit. The optic nerve or second cranial nerve is the sensory nerve of sight. The nerve arises from the ganglion cells in the retinawhich converge to form the optic nerve. The nerve passes backwards and medially and runs through the optic canal, to enter the cranial cavity and thence to the optic chiasma. The optic nerve has three coverings, similar to the meninges of the brain. The outer one is tough and fibrous and blends with the sclera, the middle covering is delicate like the arachnoid matter and the inner one is vascular.
When the fibers reach the optic chiasma half of the fibers converge to reach the opposite side of the optic tract. By means of this arrangement of fibers each optic nerve is related to both sides of the brain. The visual center lies in the cortex of the occipital lobe of the brain. The eyeball is the organ of sight. It is contained in the bony orbit, and protected by appendages such as the eyelids, eyebrows, conjunctiva, and the lacrimal apparatus.
Six muscles move the eye, four straight and two oblique. These lie inside the orbit passing from the bony walls of the orbit to be attached to the sclerotic coat of the eye behind the cornea. The straight muscles are the superior, inferior, medial, and lateral rectus muscles of the eye. These move the eye upwards, downwards, inwards and outwards respectively. The oblique muscles are the inferior and superior. The superior oblique moves the eye downwards and outwards. The movement of the eyes are combined, both eyes move to right or left, up and down, etc., the nerves supplying these muscles are the motores oculi--the third, fourth, and sixth cranial nerves.
THE Eye Globe
The eyeball is generally described as a globe or sphere, but it is oval, not circular. It is about an inch in diameter, transparent in front, and composed of three layers:
1. Outer fibrous, the supporting layer.
2. Middle, vascular
3. Inner nervous layer.
The sclera is the tough outer fibrous coat. It forms the white of the eye and is continuous in front with a transparent window-membrane, the cornea. The sclera protects the delicate structures of the eye and helps to maintain the shape of the eyeball. The anterior one quarter is called the cornea; it is composed of clear tissue permitting light rays to pass through. The anterior one quarter of the globe has a different curvature than the posterior three-quarter section and because of its shape, it also bends these light rays. The posterior three quarters of the globe is formed by a white, opaque tissue known as the sclera. This outer layer of the globe is firm and forms the casing for the vital internal structures.
The internal contents of the globe can be divided into two main areas: the anterior portion --the joining of the cornea with the sclera at the limbus, and the posterior portion, extending from the limbus posterior to the optic nerve. It contains the neuroretinal and vascular elements that are essential to seeing clearly.
The anterior chamber is a space bounded by the cornea anteriorly and the iris posteriorly, with the crystalline lens behind the central iris hole, which is known as the pupil. The anterior chambers filled with a solution known as theaqueous humor. The aqueous humor is constantly changing, being formed in the posterior chamber and flowing between the back surface of the iris through the pupils and into the anterior chamber. It then filters out from the eye through a sieve like structure in the angle where the iris is attached to the cornea and then into collector channels that flow back into the venous drainage from the globe. This sieve like structure is known as the trabecular meshwork.
The posterior portion of the globe begins with a small posterior chamber bounded by the posterior surface of the iris and the anterior surface ( hyaloid membrane) of the vitreous humor. In this posterior chamber are thecrystalline lens, the lens capsule, and the zonular fibers that hold the lens in place. The aqueous humor is formed in the posterior chamber and flows between the zonular fibers and the posterior and anterior surface of the lens throughout the pupil and into the anterior chamber.
The large posterior globe has three layers: the scleral opaque shell in the choroid that contains blood vessels of varying caliber, and the neuroretina, which contains nine layers of neural and glial cells and whose outer half receives oxygen from blood vessels and capillaries of the choroid. The inner layers receive oxygen from the retinal circulation and retinal artery. The central cavity of the posterior position of the globes filled with vitreous gel. This gel is transparent and transmits rays of light that have been bent by the curvature of the cornea and crystalline lens to form an image on the retina.
The choroid or middle vascular coat contains the blood vessels, which are theramifications of the ophthalmic artery, a branch of the internal carotid. This vascular coat forms the iris with the central opening or pupil of the eye.The pigmented layer behind the iris gives it color and determines whether the eye is blue, brown, grey, etc. the choroid is continuous in front with the iris and just behind the iris this coat is thickened to form the ciliary body, thus the ciliary body lies between the choroid and the iris. It contains circular muscle fibers and radiating fibers; contraction of the former contracts the pupil of the eye.
Together these form the uveal tract, consisting of iris, ciliary body and choroid coat.
Retina, eyelids and orbit
The retina is the inner nervous coat of the eye, composed of a number of layers of fibers, nerve cells, rods and cones, all of which are included in the construction of the retina, the delicate nerve tissue conducting the nerve impulses from the retina to the optic disc, the point where the optic nerve leaves the eyeball. This is a blind spot, as it possesses no retina. The most acutely sensitive part of the retina is the macula, which colors just external to the optic disc. And exactly opposite the center of the pupil. Once the image has been formed on the retina, it is transmitted to the brain via the optic nerve, which exits through the sclera at the scleral optic nerve foramen. The optic nerve is similar to a tract in the brain and, if cut does not regenerate like peripheral nerves.
The eye lids act like curtains that protect the globe, constant blinking removes dust and grit from the surface of the cornea and conjunctiva by moving the tear film across the palpebral tissue to the inner corner of the lids and down into the lacrimal punctum, canal sac and duct. The quick reflex of the lids protects the globe from approaching objects. The lids also protect the eyes when one sleeps by preventing the cornea from drying, the lids are covered externally byskin, and internally by a soft mucous membrane . The conjunctiva, which joins the loose mucous membrane, covers the globe up to the limbus and the edge of the cornea. The mucous glands secrete mucus that lubricates the membrane and helps entrap dust particles, which roll up into a mucous wall and can usually be found as dried secretion in the inner corner of the palpebral fissure.
The orbit is a long, conical space surrounded by bone in which the eyeball, fat, muscle, and nerves are present. The fat of the orbits cushions the eyeball and permits the extraocular muscles to contract and relax, thereby, moving the globe to different directions of gaze. Nerves and blood vessels supply these muscles, and the eyeball passes through the fat in this cone.
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See how a human eye works in this video
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