The Human Eye

Human Eye
The eye is a wonderful and the most complex organ of the human body. It is strange to learn that such a small organ has so many parts. The human eye provides us with the ability to visualize the world around us. Light enters the eye through the cornea and excites special neurons on the retina. The brain receives this information and interprets it so that we are aware of what we are seeing. The parts of the eye contribute to its proper function.

A. Parts of the Human Eye

A1 Cornea The cornea is a round, transparent dome that acts as the outer window of the eye. It is the structure that focuses the light that enters the eye. It comprises five parts. All the parts work together to protect the eye and help in the proper working of the cornea as a whole.

A2 The Lens The lens is that part of the human eye that is located immediately behind the iris. It is transparent, elastic and crystalline. Its role is to focus the light and move towards the retina.

A3 The Uvea
The uvea forms the center of the eyeball. It is made up of three parts, choroid, ciliary body and iris. The choroid is a thin membrane that is placed between the outer protective sclera and retina. Its function is to prevent the rays of light from bouncing off on the back side of the eye. Malfunctioning of the choroid may cause the formation of confusing images. The role of ciliary body is to assist in the adjustment of the shape of the lens. The iris is described as a separate part in this section of the article.

A4 The Iris The colored part of the eye is known as iris. It is present in the eye in the form of a thin diaphragm. The iris lies between the cornea and the crystalline lens. The color is due to the presence of a pigment. It is the iris that gives your eyes a particular color. The basic iris colors are blue, green and brown. Majority of humans have varying shades of these colors. It is composed of connective tissues and smooth muscle fibers. The composition of the iris enables it to dilate or contract the pupil, which in turn controls the amount of light that falls on the retina.

A5 The Retina The retina is the innermost layer of the eye. It consists of nerve tissue that senses the light entering the eye. Its function is to send impulses through the optic nerve back to the brain, where it gets translated into the images that we see. There are four types of light-sensitive receptors present in the retina. These are rods and three different types of cones. Some cones absorb long-wavelength, some absorb middle-wavelength and the rest absorb short-wavelength.

A6 The Pupil The hole in the center of the eye through which the light passes, is called the pupil. The pupil gets bigger and smaller depending on the amount of light falling on the eye.

A7 The Optic Nerve The continuation of the axons of the ganglion cells in the retina is known as the optic nerve. It connects the eye with the brain. The optic nerve emerges from the back of the eye, travels through the skull and stops inside the skull bone. From the skull bone, the nerves move through the lateral geniculate body, the internal capsule and ends up at the back of the brain. This part of the brain is known as visual cortex. It is responsible for receiving information from the eyes and interpreting it. A8 The Sclera The sclera is the whitish, opaque part of the eye, which is connected to the cornea. Its role is to provide protection and meet the purpose of attachment for the extra ocular muscles that enables eye to move.

A9 The Vitreous Humor It is the jelly like substance that is present within the interior chamber behind the lens. It is that part of the human eye whose role is to provide pressure inside the eye and keep it inflated. A10 The Conjunctiva The conjunctiva lines the inside of the eyelids and covers the sclera (white part of the eye). A11 The Fovea The fovea is the center most part of the macula. This tiny area is responsible for our central, sharpest vision. A healthy fovea is key for reading, watching television, driving and other activities that require the ability to see detail. Unlike the peripheral retina, it has no blood vessels. Instead, it has a very high concentration of cones (photoreceptors responsible for color vision), allowing us to appreciate color.

B. Eye effects
Short sight (myopia) and long sight (hyperopia) are common conditions, both caused by the cornea and lens not focusing properly on the retina.
Short sight is where the eyeball is elongated or the lens is too thick, causing the image to focus in front of the retina.
Long sight is where the eyeball is too short or the lens too thin, causing the image to focus behind the retina.

D. Conclusion Our eyes are one of God’s gifts and are very important to us. We can’t see anything in this wonderful world without our eyes. So we must take good care of it before it’s too late.