Anatomy of Human eye

Take a look around the room that you are in. Notice how the various images and colors that you see update constantly as you turn your head and re-direct your attention. Although the images appear to be seamless, each blending imperceptibly into the next, they are in reality being updated almost continuously by the vision apparatus of your eyes and brain. The seamless quality in the images that you see is possible because human vision updates images, including the details of motion and color, on a time scale so rapid that a "break in the action" is almost never perceived. The range of color, the perception of seamless motion, the contrast and the quality, along with the minute details, that most people can perceive make "real-life" images clearer and more detailed than any seen on a television or movie screen. The efficiency and completeness of your eyes and brain is unparalleled in comparison with any piece of apparatus or instrumentation ever invented. We know this amazing function of the eyes and brain as the sense of vision.

Eye Anatomy and Function

Human anatomy has been studied since ancient times. For over 1400 years our understanding of anatomy was based on theories of the Greek physician, galen of Pergamum (130-200 AD). However an accurate and comprehensive understanding of human anatomy was delayed until the Renaissance period, primarily because dissections and autopsies were forbidden by most religions. One of the first systematic studies of human anatomy which involved actual examination and dissection of the human body, was carried out by Andreas Vesalius (1514-1564). As a result of his extensive work, many of the previous misconceptions of Galenic medicine were corrected. The accumulated research of scientists over many hundreds of years has led to an excellent understanding of human anatomy

A sketch of the anatomical components of the human eye, as we now know it, is shown in Figure 1. The main structures are the iris, lens, pupil, cornea, retina, vitreous humor, optic disk and optic nerve. A discussion of the role of each component will not be presented here. These details are covered in most high school biology books and even in many sites on the World Wide Web. For example, try "the eye" Instead, we will examine the growth of the understanding of the eye's function.
A realistic understanding of the function of the components of the eye began around the 17th century, after the gross anatomy of the eye had been firmly established. It was realized in the 17th century that the retina, not the cornea as was previously thought, was responsible for the detection of light. Johannes Kepler of Germany and Renee Descartes of France, both prominent physicists of their time, made many advances in understanding vision. Much of their work applied the physical concepts of light rays and geometric optics to the vision process. Kepler first proposed that the lens of the eye focuses images onto the retina.

A few decades later Descartes demonstrated that Kepler was correct. In a landmark experiment, Descartes surgically removed an eye from an ox and scraped the back of the eye to make it transparent. He then placed the eye on a window ledge as if the ox were looking out of the window.

He looked at the back of the
eye he and saw an inverted image of the scenery outside! Descartes correctly postulated that the image was inverted as a result of being focused onto the retina by the eye's lens.
Around the beginning of the 19th century Thomas Young, a prominent physicist and physician, carried out a number of studies on the eye that resulted in an understanding of how the lens focuses images onto the retina. He also showed that astigmatism results from an improperly curved cornea. We now understand that a number of vision disorders, including both near- and far-sightedness, also result from an improperly curved cornea. The lenses in eyeglasses function by correcting for the improper corneal curve.
We now know the basic function of the components of the human eye and how they participate in the vision process. Light that reflects off of objects around us is imaged onto the retina by the lens. The retina, which consists of three layers of neurons (photoreceptor, bipolar and ganglion) is responsible for detecting the light from these images and then causing impulses to be sent to the brain along the optic nerve. The brain decodes these images into information that we know as

all parts of the eye

The eye is made up of three distinct layers around a fluid filled central cavity. The outer layer, the .sclera (the white and cornea), is a protective layer.

The sclera can be affected by episcleritis, which involves the white of the eye, or keratopathy, which affects the cornea. The inner layer, the retina, is the sensory part of the eye, used to collect light.
The central layer, the uvea, is the vascular layer. It has three parts: the iris, the ciliary body, and the choroid. It is in these three parts of the uvea that most IBD related inflammatory conditions occur. Collectively, these conditions are known as Uveitis.

A doctor sutures up after retinal repair work in 1992 in the United States. It is widely believed that sight is the most complex of the five senses. It is also often thought to be our most valued, so much so that scientists are engaged in a constant endeavor to fully understand sight so that they may better fight the seemingly endless battle against blindness.

EYE SURGERY OF STRABISMUS REPAIR IN WASHINGTON












eye surgory

Human eye and orbital anatomy, superior view

Trachoma


Trachoma, also called granular conjunctivitis or Egyptian ophthalmia, is a contagious, chronic inflammation of the mucous membranes of the eyes, caused by the bacterium Chlamydia trachomatis. It is characterized by swelling of the eyelids, sensitivity to light, and eventual scarring of the conjunctiva and cornea of the eye Trachoma is a disease associated with poverty and unhygienic conditions. It is most common in hot, dry, dusty climates in the developing world where water isscarce and sanitation is poor. Trachoma is the most common infectious cause of blindness in the world. It has two stages. The first stage is active infection of the conjunctiva by the bacterium C. trachomatis. The conjunctiva is the clear mucous membrane that lines the inside of the eyelid and covers the white part (sclera) of the eye. This stage is highly contagious.

TAcquiring trachoma does not provide immunity against re-infection, so repeat infections are the norm in many communities where the disease circulates continuously among family members. The frequency of active infection peaks in children ages three to five. In some communities, as many as 90 percent of children under age five are actively he second stage involves damage to the cornea, the transparent covering of the front of the eye. After repeated infections, the eyelids swell and the eyelashes begin to turn inward so that they scratch the cornea every time the individual blinks. This scratching is painful, and it scars the cornea, eventually resulting in the cornea becoming opaque. Individuals are often blind by middle age. Repeated, extended, untreated periods of infection are required for blindness to occur. An occasional, treated infection does not result in blindness.








The key for the various tissues:1. Cornea- composed of 5 layers, epithelium, Bowman's layer, stroma (the thickest portion), Descemet's membrane and the endothelium.2. Lens- composed of an anterior lens capsule, epithelium, cortex nucleus and posterior capsule.3. Iris- the white stroma is sandwiched between the light brown anterior border layer and the dark brown posterior pigmented layers
4. Sclera- the white tunic protects the inner structures. Thinnest over the insertion of the rectus muscles, the sclera is prone to rupture at this site from trauma.5. Macula (fovea just below the number). This is the area of central and color vision. Acuity is greatest in this region.6. Optic Nerve Head (notice the adjacent retinal blood vessels).7. Retinal vessels supply most of the retina. Choroidal vessels supply the photoreceptors and the underlying choroid.8. Vortex Veins drain the choroid and as indicated, the coalescence of orange vessels that form a whorled appearance.More detailed information can be found in our links.

cross cut of the human eye






As shown in the photograph above- the vitreous base is pigmented. The gross-dark pigmentation begins on the anterior border of the vitreous base (VB).