The Eye is the organ of sight. Eyes enable people to perform daily tasks and to learn about the world that surrounds them. Sight, or vision, is a rapidly occurring process that involves continuous interaction between the eye, the nervous system, and the brain. When someone looks at an object, what he/she is really seeing is the light that the object reflects, or gives off.
This reflected light passes through the lens and falls on to the retina of the eye. Here, the light induces nerve impulses that travel through the optic nerve to the brain, where it makes an image of the object, and then that image is passed on to muscles and glands.The eye is well protected. It lies within a bony socket of the skull. The eyelids guard it in front. They blink an average of once every six seconds. This washes the eye with the salty secretion from the tear, or lachrymal, glands.
Each tear gland is about the size and shape of an almond. These glands are located behind the upper eyelid at the outer corner of the eye. After passing over the eye, the liquid from the gland is drained into the nose through the tear duct at the inner corner of the eye.Heavy laughter or crying causes muscles in the upper eyelid to squeeze the lachrymal gland. This produces tears that flow too fast to be drained away. The eyelashes catch many flying particles that otherwise would enter the eye.
As further protection, the eyelids automatically close when an object suddenly moves close to the eye.Parts Of the EyeThe eye is made of 3 coats, or tunics. The outermost coat consists of the cornea and the sclera. The middle coat contains the main blood supply to the eye and consists of the choroid, the ciliary body, and the Iris. The innermost layer is the retina.Cornea and ScleraThe Sclera, or the white of the eye, is composed of tough fibrous tissue. On the exposed area of the eye the scleral surface is covered with a mucous membrane called the conjunctiva.
This protects the eye from becoming dry.The Cornea, a part of the sclera, is the transparent window of the eye through which light passes. The focusing of the light begins in the cornea.Behind the Cornea is a watery fluid called the aqueous humor. This fluid fills a curved, crescent shaped space, thick in the center and thinner toward the edges. The cornea and the aqueous humor together make an outer lens that refracts, or bends, light and dire...
... middle of paper ...
...he cornea is deformed so that its surface is oval instead of spherical. Light rays are distorted at the entrance of the eye. This produces a blurred image and is known as astigmatism. To correct it, glasses are given a nonspherical or cylindrical curvature. Cross-eyes and walleyes are produced when both eyes do not work together because of weakness of the eye muscles.
The images formed on the two retinas are so unlike that they cannot be blended in the brain. Thus, a double image is perceived. The condition is known as diplopia, or double vision. Prismatic lenses are prescribed to correct this defect.Imperfections in the cones of the retina, resulting from heredity or disease, cause defective color vision. This is known as color blindness, or Daltonism. In total color blindness, everything appears in shades of gray.
In its more common from, color blindness is the inability to distinguish between reds and greens.Persistent headaches, blurred vision, and painful inflammation of the eyelids are symptoms that may indicate serious eye disorders. Particles lodged in the eye should be removed without delay. Glasses are prescribed to strengthen vision and to reduce strain and fatigue.
Glaucoma is a disease of the eye and it is fluid pressure within the eye rises and if the eye is left untreated the patient might lose vision or maybe even blind. But this disease is generally affects both eyes but although one of their eyes may have more severe signs or symptoms then the other eye. When you have glaucoma there are small spaces in the front of the eye and they are called anterior chamber. There is clear liquid that flows in and out of the anterior chamber and the fluid nourishes and bathes nearby the tissues. And if the patient has glaucoma the fluid dose not drain like it should drain but the fluid drains out of the eye. And this may lead to fluid build up and pressure inside the rises of the eye. Unless the pressure is brought down and controlled and the optic nerves and some of the other parts of the eye might become damaged leading to ...
Sclera is an outer fibrous layer which mainly provides the mechanical stability to protect the eye and its sensitive optical apparatus. Sclera is mainly composed of collagen and elastic fiber and their irregularity gives sclera an opaque appearance. The most important function of sclera is to offer resistance to internal and external forces and to provide attachment for the extraocular muscle insertions. The scleral surface area in humans is
The human eye is an organ that allows a person to see, the sense of sight. The eye is composed of several parts including the cornea, lens, pupil, retina, optic nerve etc. There are two portions the eye is broken into, the front third is the anterior segment and the other two thirds is the posterior segment. The anterior segment includes the lens, cornea, iris, and ciliary body. The posterior segment of the eye essentially is the back portion of the eye. In detail, the posterior segment is the portion of the eye behind the lens that includes the retina, macula, optic nerve, choroid, and vitreous humor. There are many diseases that affect the eye and those in particular affecting the posterior segment will be discussed in detail.
As humans age, they frequently develop a condition known as presbyopia. This condition decreases the person's ability to focus sharply on those object which are nearby and is the result of the lens of the eye hardening. In addition, astigmatism requires a person wear prescription eyeglasses and/or contact lenses. Astigmatism arises when the curvature of the eye is irregular. The eye is normally shaped liked a soccer ball or basketball. With astigmatism, it takes on a more oval shape and resembles a football. Due to the irregular curvature, the eye processes light differently and leads to blurred vision. The degree of blurriness is determined by the degree of
Most of the eye is filled with a clear gel called the vitreous. Light projects through the pupil and the lens to the back of the eye. The inside lining of the eye is covered by special light-sensing cells that are collectively called the retina. The retina converts light into electrical impulses. Behind the eye, the optic nerve carries these impulses to the brain. The macula is a small extra-sensitive area within the retina that gives central vision. It is located in the center of the retina and contains the fovea, a small depression or pit at the center of the macula that gives the clearest vision. The blind spot is at the exit point of the optic nerve, at this point there are no rods or cones, and so all the light directed here are of no use. Eye color is created by the amount and type of pigment in the iris. Multiple genes inherited from each parent determine a person’s eye color. Though the eye is such a wonderful organ, it is also prone to diseases, infections, and other problems that could be minor or major, and could lead to blindness or poor
The four main components of the eye that are responsible for producing an image are the cornea, lens, ciliary muscles and retina. Incoming light rays first encounter the cornea. The bulging shape of the cornea causes it to refract light similar to a convex lens. Because of the great difference in optical density between the air and the corneal material and because of the shape of the cornea, most of the refraction to incoming light rays takes place here. Light rays then pass through the pupil, and then onto the lens. A small amount of additional refraction takes place here as the light rays are "fine tuned" so that they focus on the retina.
Amblyopia is a condition in which visual acuity in one eye is greatly reduced. It is caused by lack of stimulation or disuse during visual development (Rose, 1998). Because the eye is not fully developed at birth (Jarvis, 1992, as cited in Rose, 1998), infants need stimulation to complete the visual neural pathway. When one or both eyes are inhibited, for example due to misalignment of one eye (strabismus) or a large difference in refractive power between two eyes (anisometropia), the neural pathway for the inhibited eye develops abnormally, or does not develop at all. At approximately six years of age eye development is complete (Stager, 1990, as cited in Rose, 1998). Before visual development is complete amblyopia can be treated. If it is caught and treated at an early age, normal vision can be preserved (Rose, 1998).
Fluid circulating inside the front portion of the eye is produced by a structure called the ciliary body, which is located behind the iris. This fluid moves through the opening of the pupil, passes into the space between the iris and the cornea, and drains out of the eye through a tissue called the angle. With glaucoma, the passing of fluid through the angle is either reduced or suddenly stops, and amounts of fluid inside the eye increase. This high fluid pressure hurts the nerve fibers and the eye's optic nerve and causes blind spots. It may lead to blindness in some cases.
Laila confirms that her friends have ordered pizza using her visual system. Through the sensation of light, sensory information is processed and Laila is then able to see the pizza. The pupil absorbs light, by allowing light to enter the eye, and light will then be transferred to the lens. The lens is responsible for refracting light and focusing the light inside of the eye, also known as the retina. The second cranial nerve, or optic nerve, is responsible for carrying the visual signal from the eye to the optic chiasm. The optic nerve, or second cranial nerve, is located in the back of the eye. This cranial nerve transfers visual information to visual centers in the brain through many electric impulses. The optic chiasm has temporal fibers that travel ipsilaterally as nasal fibers transmit information contralaterally, to the opposite side of the associated visual field. The visual cortex can then process sensory information from the opposite eye. Laila’s blind spot is where the optic nerve begins and there are no rod or cone cells in the optic nerve. The brain has to try to compensate for the lack of photosensitive
the cornea and the sclera. The cornea is what covers the iris, and is the
An inspection of the modern animal phyla will reveal that eyes are just as diverse as they are complex. Some organisms like the rag worm have pigmented cup eyes while other like he box jellyfish have two lens eyes and two pairs of pigment pit eyes. To account for the diversity in eye structure, we must first examine the eye ‘prototype’, the original structure that was acted upon by evolution. The simplest organ that can be considered an eye is composed of a single photoreceptor cell and a single pigment cell, without any lens or other refractive body (Arendt, 2003). Such organs are know as eyespots, and...
One sub-system under the sensory system is the visual system; the main sense organs of this are the eyes. The eye is the sensory organ that allows us to detect light from external stimuli. When a light ray is detected, the eye converts these rays into electrical signals that can be sent to the brain in order to process the information and giv...
Nearsightedness also known as myopia, is a disorder where one can see clearly close up, but see blurry at a distance (for example, not being able to read the blackboard but being able to read a book). This occurs when the eyeball is too long or the cornea is too curved to focus on the retina.
The incredible thing about the human eye is that it can see objects to as far as 2 miles long.That’s almost 35 football fields! Let’s consider the mechanics of the eye. The eye is a clear ball with water-like fluids in there.You have the front of the eyeball which is translucent called the cornea. It’s extremely thin and its job is to protect the eye by refracting light that comes through. The next part of the eye is the pupil, which mostly everyone knows about.It is the black portion in your eye. Did you know that it gets its color from when light entering the eye is absorbed and it doesn’t leave the eye. You may also notice that when you’re looking at the pupil, you can see a different colored circle in them. This is called the iris, and it varies among everyone. Your actual eye color is determined by a pigment in the iris.The genes from your parents set a human’s eye color. The iris’s job is to widen or close depending on how bright or dark it is. If its bright and the sun is basically beaming down on you, the iris will adjust so your pupil will get smaller to only let a certain amount of light in. If you’re in the dark, your iris adjusts so your pupil will get bigger so a greater...