The Human Eye

The oculus is a rather sm solely let on of the dust that makes up seventy percent of the gays total sensory ability. That is why we chose to describe the centre center. separately agency of the gist schools together as a whole. Within and outside of the midpoint there ar legion(predicate) working stops functioning a large the clock.. The cornea is a real serious fork of the fondness, but you can hardly see it beca economic consumption its make of release tissue. Like glass, the cornea gives your centre of attention a window in which to view the world. The a cornea is a diaphanous tissue c overing the front of the eye. The cornea covers both the educatee and he masthead eye, and it is bring outially responsible to way percipient.The cornea is part of the extraneous structure of the ball. The external spirit level of the eyeball is formed by the cornea, and the sclerotic coat. The cornea is a dome-shaped structure. The cornea does not have any blood vessels that is why it appears illume. The cornea does have steel. The cornea is the first off and most powerful crystalline lens in the eyes middleal schema. The cornea is the first part of the eye to focus. When a ray of clean- nutrition hits the eye, the cornea is the first structure the hoy encounters. Then the enlighten rays travel by means of your eye through a hole called the educatee.As light rays from an object enter your eye, they ar hang inward by the cornea and lens. Light rays are focused through the transparent cornea and lens. Light rays focused by the cornea and lens produce an image on the retina that is top side down. The cornea is made up of five layers the epithelium, Bowmans layer, the stroma, Descements membrane, and the endothelium. The cornea obtains oxygen through absorption from the tear film layer, and from the aqueous inclination. The part that flow over the cornea help to abide by it nourished and moist. key out retch The former chamber lies in the midst of the flag and the back surface of the cornea. at that place are 3 chambers of runny in the eye. The anterior chamber, which is between the cornea and iris. The tin can chamber, which is between the iris and lens. And, the vitreous chamber, which is between the lens and the retina. The fluid filled substance is called the aqueous humor. It is a clear fluid that fills the anterior chamber and the posterior chamber of the anterior cavity of the eye. The aqueous humor bathes the lens and gives nourishment to the lens. The aqueous humor is produced by the ciliary body. piddle tramp discusoverframe The colored part of the eye is called the iris.It controls light levels inside the eye similar to the hole on a camera. The round opening in the center of the iris is called the pupil). The iris is embedded with exact bodybuilders that dilate (widen) and constrict (narrow) the pupil size of it. The sphincter brawn lies round the very edge of the pupil. In bright lig ht, the sphincter contracts, causing the pupil to constrict. The dilator tendon runs radically through the iris, analogous spokes on a wheel. This muscle dilates the eye in dim lighting. The iris is flat and divides the front of the eye (anterior chamber) from the back of the eye (posterior chamber).Its color comes from microscopic pigment cells called melanin. The color, texture, and patterns of each persons iris are as unique as a fingerprint. The pupil is the relentless circle in the center of the iris. But, the pupil is really a clear opening. The pupil appears black because the light which the pupil allows to enter the eye is absorbed on the retina and does not exit the eye. Light enters the eye through the cornea it then(prenominal)(prenominal) travels through the opening called the pupil. Light then enters the eyes lens. The pupil changes size in order to adapt to the quantity of light rays that reach it.The pupils constrict in response to increased light, this makes y our pupils smaller. When the pupils are smaller, it allows in as little light as possible. The pupil dilates in response to decreased light, this makes your pupils larger. When the pupils are larger, it allows in as much light as possible. The pupil size is stubborn by a reflex action that allows less light into the eye during bright conditions, so the person is not dazzled. The pupil size is headstrong by a reflex action that allows much light into the eye during dim conditions this will make vision possible for the person.To see how this works, use a small flashlight to see how your eyes or a friends eyes respond to the changes in brightness. The pupils will get smaller when the light shines near them and theyll open wider when the light is gone. cotton upframe drawframe drawframe * Dilated* Pupil * Constricted* Pupil The lens is part of the internal structure of the eyeball. The lens is transparent. The lens is the flexible curved part of the eye that sits behind the iris and in front of the vitreous humor. The lens of the eye is made of mostly water and protein. Light which passes through the pupil opening, will nter the lens. The lens focuses light rays on the back of the eye. The lens purpose is to focus images onto the retina. It works like the lens of a camera that records the picture. The lens turns the images upside down. Then the picture is transmitted by the optic facial expression to the brain. In young people, the lens changes shape to adjust for close or hold vision. The lens changes shape when looking at objects at several(predicate) distances to clutch the images in focus. The lens changes its shape by bending. The adjustment of the lens of the eye is similar to the focusing of a camera.This adjustment of the lens is known as accommodation. As we become older adults, the lens gradually hardens, and it becomes harder for the lens to accommodate. drawframe drawframe The Ciliary Body and the Ciliary Muscle, separates the sedimentary Humor , the fluid and, the Anterior Chamber. The vitreous humor is located in the posterior chamber of the eye. The posterior chamber is a space behind the iris and it is in front of the retina. This space behind the lens is filled with a jellylike substance called the vitreous humor. The vitreous humor helps to shape the eyeball.As we age and get to be older adults, the vitreous humor changes from a gel to a liquid like fluid and it gradually shrinks and separates from the retina. drawframe The retina is the innermost layer of the eye. The retina is made up of dickens separate an optical part in the fundus of the eye that is sensitive to light, and a un cut back pigmented part that lines the ciliary body and iris. The light-sensitive neurons are arranged in three layers the first layer is made up of rods and cones and the other two transmit impulses from the rods and cones to the optic organisation.The rods are sensitive to dim light of a variety of wavelengths, and the cones are sens itive to bright light of more restricted wavelengths and are responsible for color vision. Visual acuity is greatest in the central part of the retina. drawline drawframe drawframe The retina is a stack of several neuronal layers. Light is surd from the eye and passes across these layers (from left to right) to hit the photoreceptors (right layer). This causes a chemical transformation of light to nerve impulse to the bipolar and horizontal cells (middle yellow layer).The luff is then transmitted to the amacrine and ganglion cells. This pattern of spikes determines the raw input from the eyes to the brain. The optic disc is a whitish spot on the retina. The optic disc is called the blind spot. The optic disc is the spot on the retina that the optic nerves come from. The optic disc marks the point where nerve fibers vary the eye. The optic disc lacks light sensitive cells. There are no sensory cells here that are why it creates a blind spot. The macular area lutea lutea is an i rregular yellowish spot near the center of the retina.The macula lutea lies fairly below the optic disc. The macula lutea is part of the retina and it is the most light sensitive. The size of the macula lutea is 7mm or about ? inch. The macula lutea is responsible for our reading vision. It is this part of the retina that makes our vision 20/20. If you do not have a macula lutea, you would not be able to see. cranial case II, or more familiarly known as the optic nerve, is the nerve that controls the sense of vision. Without this the human race could not see, it acts as a passageway of the object you see, to be transferred as a skittish impulse to the brain.The part of the brain the nervous impulses are sent to is the visual cortex, this is a section of the brain where all of the information is processed. The optic nerve is formed out of axons. An axon is the farsighted processes of retinal cells at the back of the eye. These join together to form the nerve, which exits the eyeb all at a point called the optic disc. The optic nerve fibers, rebel in the retina, then enter the optic nerve which again passes through the eye socket. This then heads to the optic canal, the opening in the skull which receptors pass from the eye to the brain.The optic nerve fibers the join together to form the optic charisma, this contend in fibers allows for binocular vision, they continue until it makes contact with the lateral geniculate. The optic nerve radiates back to the visual where the image is processed. To sum this up the optic nerve carries information to the brain from the eye. This concludes the internal mechanism of the eye. Next is a word of honor of the external anatomy of the eye and components surrounding it. There are three layers of the eyeball. The external layer of the eyeball is formed by the sclera, and the cornea.The sclera is the egg white part of the eye. The sclera is continuous with the cornea. The sclera is the outermost layer, and the sclera is the thickest layer of the eyeball. The sclera has the important melody of covering most of the eyeball. The conjunctiva is a mucous secretion membrane which covers the sclera that you can see through and lines the hats as the palpebral conjunctiva, and reflects or folds back over the anterior of the eyeball, as the ocular, or in most cases this can be called the bulbar conjunctiva. The bulbar conjunctiva only covers the white of the eye not the cornea.The ocular conjunctiva is very thin, blood vessels are visible at a lower place it, when irritated the eye becomes bloodshot. When the eyelids are shut a slit like space appears between the covered eyeballs and eyelids. When you are wearing contacts, the contact lies in the conjunctivial pocket, this is where most eye medications are placed alike. The conjunctivas main job is to treasure the eye from anything that may penetrate the eye. Certain eye problems that may resuscitate to the conjunctiva include the inflammation of th e conjunctiva which is called conjunctivitis_. _Pinkeye which is probably the most familiar to people living in America.Pinkeye consist of a bacteria or virus that is, in most cases , on your hands and you do not swosh them then it is spread around the eye. All infections in this area are contagious. The sclera is also a supportive and protective layer of the eye. The sclera forms a tough shell that helps protect the inner structures of the eyeball. There are three pairs of muscles attached to the sclera. These muscles are named extra-ocular muscles. drawframe There are six extra-ocular muscles on each eye. Each muscle has a different form of movement or function in the eye.The Lateral Rectus is the muscle that moves the eye outward. The Inferior Rectus muscle is the muscle that pulls the eyeball towards the ground. The Inferior musculus obliquus externus abdominis muscle raises the eye, and pivots the eyeball outwards. The Superior Oblique muscle pulls the downwards and outwards, eon abducting the eye. The tendon-like Trochlea, acts like a pulley which the transcendent oblique muscle passes through. The Superior Rectus muscle pulls the eye upwards and inwards. The Palpebrae Superioris muscle pulls the upper eyelid upwards. The Medial Rectus muscle moves the eyes inward horizontally.The Tendinous Ring is a band of rough, fiber-filled tissue, that holds the eye muscles in place. The second layer of the eye is called the uvea. The uvea contains umpteen blood vessels and pigmented cells. The uvea is divided into three main sections the choroid, the ciliary body and the iris. The choroid extends from where the optic nerve meets the eye-ball to the front of the eye, where it forms both the ciliary body and the iris. The triplet layer is the retina. The lacrimal glands are located above each eye. The Lacrimal gland lies underneath the upper eyelid. The Lacrimal gland has the important job to produce tears.The Lacrimal gland continually produces tears that are distributed over the surface of the eyes. The tears drain through the Lacrimal canals into the Lacrimal sac and into the nose from the Lacrimal duct. The tears are constantly being made in the Lacrimal glands and through the action of blinking the tears drain. either time the eyelid blinks, it causes tears to flow from the Lacrimal glands. The tears keep the cornea moist and provide oxygen to the cornea. The tear production increases when you cry or if the eye is irritated by foreign particles. The Lacrimal gland also produces other protective fluids onto the surface of the eye. drawframe Cranial Nerve III, the oculo repulse nerve controls the eye muscles, or two-thirds of them anyway. This Nerve Mainly carries the tug fibers to the eye muscles, this controls the movement of the eye and where the eyes position is located. The oculomotor nerve contains fibers from the nervous system which constrict the pupil and also alter the lenses shape. The oculomotor nerve originates midbrain , is part of the brainstem and leaves the cranial cavity through the eye socket into the superior orbital fissure. From the superior orbital fissure, this is split into two parts, the superior and inferior divisions.Problems associated with the oculomotor nerve, are damage to the nerve, in which case all but two of the eye muscles will be paralyzed, occasionally when this happens the eyelid will drop. overly the eye will not move sideways. Cranial Nerve IV, the trochlear nerve nerve, only supplies one muscle for movement to the eye. This nerve transmits both the motor information of the eye and the sensory information of the eye. The nerve originates about midbrain, around the brainstem and finally ends up through the center of the eye socket into the superior orbital fissure. The trochlear nerve controls the muscle that moves the eye up and down.Cranial Nerve VI, is the abducent nerve, this leads to the lateral rectus muscle in the eye. The abducent nerve contains both motor fiber s and sensory fibers. The fibers of the abducent nerve originate in a part of the brainstem called the Pons. The nerve arrives at the eye socket then passes through the superior orbital fissure. This moves the eye out to the side. The eye is a important and fascinating organ. It is made up of many different kinds of tissues. Each has a very important and individualized function. Its many parts work together to form the phenomenon of sight. This allows us to perceive the world.