The Human Eye

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A Journey Through Our Eyes & The Damages To It !!!!! Please !!!! Read it and Understand Its Importance !!!!!

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Thnx Sanaullah

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very great information

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The Human Eye:

The Human Eye

INTRODUCTION:

INTRODUCTION The human eye is the organ which gives us the sense of sight, allowing us to observe and learn more about the surrounding world than we do with any of the other four senses. We use our eyes in almost every activity we perform, whether reading, working, watching television, writing a letter, driving a car, and in countless other ways.

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Most people probably would agree that sight is the sense they value more than all the rest. The eye allows us to see and interpret the shapes, colors, and dimensions of objects in the world by processing the light they reflect or emit. The eye is able to detect bright light or dim light, but it cannot sense objects when light is absent.

PARTS OF THE HUMAN EYE:

PARTS OF THE HUMAN EYE

CORNEA:

CORNEA The cornea is a clear, dome-shaped surface that covers the front of the eye. Tears that flow over it and aqueous humor in the chamber behind it keep it nourished. It allows the light to enter the eyeball. The eyeball is approximately spherical in shape with a diameter of about 2.3 cm. When you hear of eye banks and eye transplants, it is the cornea that is being replaced. The cornea can be damaged from: accidents, infections, and genetic defects. To keep it transparent the cornea contains no blood vessels.

IRIS:

IRIS This is the colored part of the eye: brown, green, blue, etc. It is a ring of muscle fibers located behind the cornea and in front of the lens. It contracts and expands, opening and closing the pupil, in response to the brightness of surrounding light. Just as the aperture in a camera protects the film from over exposure, the iris of the eye helps protect the sensitive retina.

PUPIL:

PUPIL The pupil is the hole in the center of the iris that light passes through. The iris muscles control its size. It contracts in excess light and expands in dimlight.

Ciliary Muscle:

Ciliary Muscle The eye can bring the fine print in a phone book into focus, or focus in on the moon over ¼ million miles away. The ciliary muscle changes the shape of the lens - (this is called accommodation). It relaxes to flatten the lens for distance vision; for close work it contracts rounding out the lens. Everyone will develop an eye condition called presbyopia. As we age, the ciliary muscle and crystalline lens lose their elasticity. This is why most people need reading glasses by their 40's.

EYELENS:

EYELENS It is a convex lens made of a transparent and flexible material like a jelly made of proteins. It forms of a real image of the objects on the retina of the eye

Power Of Accommodation:

Power Of Accommodation Ability of eye lens to adjust its focal length. For Young Adult P= 4D

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Near Point (Least Distance Of Distinct Vision) Its is the minimum distance at which eye can see objects very clearly without any strain. Its value is 25 cm . Far Point It is the farthest point up to which eye can see objects very clearly. Its value is ∞

RETINA:

RETINA The retina is the film of the eye. It converts light rays into electrical signals and sends them to the brain through the optic nerve. The sides of the retina are responsible for our peripheral vision. The center area, called the macula, is used for our fine central vision and color vision.

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The retina is where most the problems leading to vision loss Occur. Three of the leading causes of blindness, from retina damage, are Retinitis Pigmentosa, Macular Degeneration and Diabetic Retinopathy.

Retinitis Pigmentosa:

Retinitis Pigmentosa

Macular Degeneration:

Macular Degeneration

Diabetic Retinopathy.:

Diabetic Retinopathy .

OPTIC NERVE:

OPTIC NERVE Each optic nerve has about 1.2 million nerve fibers. This is the cable connecting the eye to the brain.

SCLERA:

SCLERA The sclera is the white, tough wall of the eye. It along with internal fluid pressure keeps the eyes shape and protects its delicate internal parts.

CHOROID:

CHOROID The choroid is a layer of blood vessels between the retina and sclera; it supplies blood to the retina. It keeps the interior eye dark.

BLIND SPOT:

BLIND SPOT The region on the retina where there is no cones a nd rods at the part where the optic nerve leaves the eyeball.

YELLOW SPOT OR MACULA:

YELLOW SPOT OR MACULA It is situated at the Centre of the retina. Its function is to form an extremely clear image.

VITREOUS HUMOUR:

VITREOUS HUMOUR The vitreous humour or vitreous humor is the clear gel that fills the space between the lens and the retina of the eyeball of humans and other vertebrates. The vitreous is the transparent, colourless , gelatinous mass that fills the space between the lens of the eye and the retina lining the back of the eye. It is produced by certain retinal cells. It contains very few, no blood vessels, and 98-99% of its volume is water with salts, sugars, vitrosin, and a wide array of proteins in micro amounts.

AQUEOUS HUMOUR:

AQUEOUS HUMOUR The aqueous humour is a clear, gelatinous fluid similar to plasma, but containing low-protein concentrations. It is secreted from the ciliary epithelium, a structure supporting the lens.It is located in, the space between the lens and the cornea.

Working Of Human Eye:

Working Of Human Eye

Sites To Visit For More Info:

Sites To Visit For More Info http://www.99main.com/~ charlief/Blindness.htm [Human Eye And Its Parts] http:// www.tedmontgomery.com/the_eye/Process_of_Vision.html [Working Of Human Eye]

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Defects To The Eye

MYOPIA:

MYOPIA Myopia is a condition of the eye where the light that comes in does not directly focus on the retina but in front of it. This causes the image that one sees when looking at a distant object to be out of focus but in focus when looking at a close object. Myopia presents with blurry distance vision, but generally gives good near vision. In high myopia, even near vision is affected, and patients cannot read without their glasses for distance.

CAUSES :

CAUSES Most nearsightedness is caused by a natural change in the shape of the eyeball. Other than the natural change in the shape of the eyeball, there are a few rare causes of nearsightedness. These are:

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Pathological myopia, in which the back of the eyeball continues to grow longer after reaching normal adult size. Secondary myopia, which may develop as a result of many conditions, including premature birth and a number of eye diseases. In some cases, nearsightedness may be caused by eye problems such as cataracts,etc .

TREATMENT :

TREATMENT There is no universally accepted method of preventing myopia.Commonly attempted preventive methods include wearing reading glasses, eye drops and participating in more outdoor activities

HYPERMETROPIA:

HYPERMETROPIA Hypermetropia , is a defect of vision caused by an imperfection in the eye causing difficulty focusing on near objects. Farsightedness occurs when light entering the eye through the lens is focused behind the retina  instead of directly on it.

CAUSES :

CAUSES Hyperopia can be caused by infections, injuries, migraines, aging or genetics. This is caused by an eye that is too short, whose cornea   is not curved enough, or whose lens sits farther back in the eye than normal. Farsightedness is also inherited.

TREATMENT :

TREATMENT Minor amounts of hyperopia are sometimes left uncorrected. However, larger amounts may be corrected with convex lenses in eyeglasses or contact lenses. Convex lenses have a positive dioptric value, which causes the light to focus closer than its normal range.

PRESBYOPIA:

PRESBYOPIA Presbyopia is a condition where the eye exhibits a progressively diminished ability to focus on near objects with age. Presbyopia’s exact mechanisms are not known with certainty; the research evidence most strongly supports a loss of elasticity of the crystalline lens, although changes in the lens’s curvature from continual growth and loss of power of the ciliary muscles (the muscles that bend and straighten the lens) have also been considered as its cause.

SYMPTOMS OF PRESBYOPIA:

SYMPTOMS OF PRESBYOPIA The first symptoms most people notice are difficulty reading fine print, particularly in low light conditions, eyestrain when reading for long periods, blur at near or momentarily blurred vision when transitioning between viewing distances .These symptoms are usually first noticed between the ages of 40 and 50.

TREATMENT:

TREATMENT Corrective lenses provide a range of vision correction, some as high as +4.0 diopter. Contact lenses can also been used to correct the focusing loss that comes along with presbyopia . Controversially, eye exercises have been touted as a way to delay the onset of presbyopia, but their effectiveness has not been demonstrated in medical research .

CATARACT:

CATARACT The lens of the eye is normally clear. It acts like the lens on a camera, focusing light as it passes to the back of the eye. Until a person is around age 45, the shape of the lens is able to change. This allows the lens to focus on an object, whether it is close or far away. As we age, proteins in the lens begin to break down and the lens becomes cloudy. What the eye sees may appear blurry. This condition is known as a cataract.

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Factors that may speed up cataract formation are: Diabetes Eye inflammation Eye injury Family history of cataracts Radiation exposure Smoking Surgery for another eye problem Too much exposure to ultraviolet light (sunlight) In many cases, the cause of cataract is unknown.

SYMPTOMS:

SYMPTOMS Adult cataracts develop slowly and painlessly. Vision in the affected eye or eyes slowly gets worse. By age 75, most people have cataracts that affect their vision. Visual problems may include the following changes: Being sensitive to glare Cloudy, fuzzy, foggy, or filmy vision

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Difficulty seeing at night or in dim light Double vision Loss of color intensity Problems seeing shapes against a background or the difference between shades of colors Seeing halos around lights

TREATMENT:

TREATMENT The following may help people who have an early cataract: Better eyeglasses Better lighting Magnifying lenses Sunglasses

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As vision gets worse, you may need to make changes around the home to avoid falls and injuries. The only treatment for a cataract is surgery to remove it. Surgery is done if you cannot perform normal activities, such as driving, reading, or looking at computer or video screens, even with glasses.

ASTIGMATISM:

ASTIGMATISM Astigmatism is a type of refractive error of the eye. Refractive errors cause blurred vision and are the most common reason why a person goes to see an eye professional.

Causes, incidence, and risk factors:

Causes, incidence, and risk factors People are able to see because the front part of the eye is able to bend (refract) light and point it to the back surface of the eye, called the retina. Changes in the length of the eye, or the shape of either the lens or the cornea make it more difficult for the eyes to focus light. If the light rays are not clearly focused on the retina, the images you see may be blurry.

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With astigmatism, the cornea (the clear tissue covering the front of the eye) is abnormally curved, causing vision to be out of focus. The cause of astigmatism is unknown. It is usually present from birth, and often occurs together with nearsightedness or farsightedness. Astigmatism is very common. It sometimes occurs after certain types of eye surgery, such as cataract surgery.

SYMPTOMS:

SYMPTOMS Astigmatism makes it difficult to see fine details, either close up or from a distance.

TREATMENT:

TREATMENT Mild astigmatism may not need to be corrected. Glasses or contact lenses will correct astigmatism. Laser surgery can help change the shape of the cornea surface to correct astigmatism, along with nearsightedness or farsightedness.

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