Saturday, December 16

The Eye The Organ Of Sight

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The eye is the organ of sight. Consisting of structures that send image to back of eye onto the retina and nerve networks convert the image to electrical impulses. Both eyes work to form clear images form on each retina. The image is sharpened by accommodation by focusing with the automatic process. The pattern of light on the retina stimulates a flow of impulses along the optic nerve to the brain. The two optic nerves pass into the skull almost cross over and extend back on the underside of the brain then through the visual cortex.

The eyeball are located in pads of fat within the boney eye socket (for protection) and is moved by six delicate muscles. The movement of these muscles are coordinated by nerve networks in the brain stem. The tough outer coat is known as the sclera or whites of eyes. The outer coat the cornea is transparent and protrudes a small amount.

The human eye protected by the orbital socket of the skull, eyelashes, eyebrows, and eyelids. They are continually bathed in fluid by tears from the lacrimal glands. The tears empty into the lacrimal duct thus our nose also is affected by tears. Lacrimal secretions have an antibiotic property that cleanse and moistens eyes.

At the border of each eyelid are glands that oil the eye. An infection of this gland is called a sty.

The conjunctiva (thin membrane that lines the eye)secretes mucus which lubricates the eye. Each eye super imposition of images in both eyes allowing 3D vision of length,width, and depth.

The wall of the eye is made up of three concentric layers each with a function. the three layers are retina(light sensitive layer) , sclera (whites of the eye), and choroid (blood vessels that nourish the eye and non-reflective pigment) .

 

 

 

Some Eye disorders are caused by:

Congenital defects

Infection

Impaired blood supply (narrowing, blockage and inflammation)

Tumors (Malignant melanoma of middle layer of eye)

Nutritional Disorders (vitamin deficiencies paticularly vitamin A)

Autoimmune disease (the body attacks its own tissues)

Macular degeneration ( aging of eye)

Glaucoma (fluid that keeps shape of eye is raised)

Retinal detachment (retina lifts away from underlying layer)

Ametropic (a re-tractive error)

Presbyopia (inability to focus on close objects)

Hyperopia (eyeball shorter than normal)

Myopia (eyeball is elongated)

Amblyopia (Reduction or dimness of vision)

Astigmatism (irregular curvature of the cornea or lens)

Diplopia (blurred vision)

Strabismus (cross eyes)

Strabismus (squint or mal-alignment of the eyes)

Cataracts (opacity of the lens of the eye)

Nystagmus (rapid uncontrollable movement )

Retinoblastoma (malignant tumor of the retina)

Albinism (absence of pigment)

Conjunctivitis (pink eye)

Corneal Infections

Endophthalmitis (infection within the eye)

Malignant melanoma

Xerophthalmia (dryness of cornea and conjunctiva)

Keratomalacia (cornea softening and destruction)

Uveitis (inflammation of the uveal tissue- iris, cillary, and choroid)

Ankylosing spondylitis (crippling and deforming arthritis)

Sarcoidosis

Lazy eye (normal vision failed to develop)

Night blindness makes it difficult to see at night. The rod cells in the retina affect this condition. Color blindness is a hereditary characteristic. There are three types of cone cells in the retina related to the primary colors of blue, red, and green. These cone cells are affected in color blindness.

As we age we lose elasticity, opacity of lens, and atrophy of the ciliary muscle and it causes the ability to focus on the fine details to become difficult. As we get older we need more time to focus and for eyes to adjust from light to dark thus we lose night vision.

Peripheral vision and depth perception also decrease with age. Just to be able to walk in crowded places and to drive, an adequate visual field is necessary. Also as we age miscalculations about height of objects and distances lead to mobility problems. Falls are more likely to happen. Also the lenses lose visual acuity because of changes in the lenses. Age also causes more appearances of macular degeneration, cataract formation, and glaucoma.

 

 

 

 

 

 

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