By LiveScience Staff posted: 15 January, 2006 6 am ETNature has many ways of making it hard for people to see. Here are eye disease prevalence numbers in adults 40 years and older in the United States, based on data from 2000:
Cataract (20.5 million)—a clouding of the eye’s usually clear lens and is the leading cause of blindness in the world.
Age-related macular degeneration (1.8 million)— a disease that damages the eye’s macula, located in the center of the retina, causing a loss of sharp, central vision needed for tasks like reading and driving.
Glaucoma (2.2 million)—a disease that gradually damages the optic nerve that carries visual signals from the eye to the brain. As much as half of all people with glaucoma are unaware they have it because only after a significant amount of nerve damage does a person loses vision.
Retinal diseases (diabetic retinopathy and retinitis pigmentosa)—a group of hereditary disorders in which the rod and cone cells in the retina deteriorate causing impaired or loss of vision.
• Diabetic retinopathy (4.1 million)
• Retinitis pigmentosa (50,000 to 100,000)
Source: National Eye Institute/NIH
Cataract
It is the clouding of the normally transparent lens in the eye. It lowers the degree of transparency and thus the objects seen will become blur.
Cataract is a common cause of poor vision. It usually develops gradually when people get older, but this can also happen to youngsters or be present at birth. In the early stages of the cataractous process, it is a normal part of aging and is not considered as a disease at all. As we age, chemical changes occur in the human lens that render it less transparent. For mild cases, it hardly affects vision, but for severe cases, only light and dark can be seen. Without effective treatments, cataracts account for as much as 50% of the world's mass blindness and it is one of the world's leading causes of blindness.
Common symptoms:
• diminished vision
• double vision
• newly acquired ability to read without glasses
• frequent changes in eyeglass prescription (for serious cases)
• poor vision in bright light and improved vision in dim light
• decrease in sensitivity to color
Causes:
• Aging
• Long duration of diabetes
• Injury to lens
• Congenital
• Glass blowers
• Other eye diseases
• Dehydration
• Low levels of calcium
• Continuous doses of cortisone for prolonged periods
• Cigarette smoking
• Treatment:
by surgery -- the operation involves the removal of the clouded lens from the eye and the implant of an artificial lens. There are 3 types of surgery: 1) posterior chamber implants 2) anterior chamber implants 3) iris-supported implants. These operations may leave an optical error that can be corrected by eyeglasses, contact lenses, or by implanting an intraocular lens. In Hong Kong, the rate of success in this operation is 95%. The complications of it includes internal bleeding of the eye, glaucoma, retinal detachment.
Glaucoma
It is an ailment that includes any eye diseases which cause an increase in pressure in the eye. The eye is filled with a clear fluid -- humor -- which helps maintain the eye's shape and nourishes the lens and cornea. The ciliary body continuously secretes new humor and the excess is drained through the front of the eye. In glaucoma, the fluid does not drain away properly, the pressure inside the eye accumulates, pinching the blood vessels to the optic nerve. As the nutrients cannot be transported the nerve cells via the blood vessels, the nerve cells slowly die, causing progressive loss of vision which can lead to total blindness. This results in visual loss by damaging the optic nerve and retina. Unfortunately, glaucoma is usually detected when the patient has already suffered vision loss and this visual loss is irreversible, no medical treatment or surgical operation can restore the vision.
Types of glaucoma
The four different types of glaucoma
1) Primary open angle glaucoma ( Chronic simple glaucoma )
This is the most common form of glaucoma and it's believed to be inherited and is almost always bilateral. At the early stage, most of the glaucoma patient do not have any symptoms and it is very difficult to be detected. It is usually be detected through regular eye examinations. At the later stage, the optic nerve has already been destroyed, the patient's vision will become narrower and narrower. Finally, objects beyond the central vision can not be seen, as if looking through a cylinder, with diminishing vision, the patient will finally become blind.
With advancing age, open angle glaucoma is not a disease. With age, the trabecular meshwork becomes less able to drain aqueous from the anterior chamber. As a result, the intraocular pressure increases. When the patient has lost all vision from glaucoma, the patient is suffering from Absolute Glaucoma which is often painful.
2) Primary angle closure glaucoma ( Congestive glaucoma )
Angle closure glaucoma is a common blinding disease in adults which is suspected when the ocular media is clear and peripheral or central vision is reduced. An acute and painful glaucoma, primary angle closure glaucoma results when normal iris suddenly blocks the trabecular meshwork and thereby outflow of aqueous. This may occur in an eye with an abnormally shallow anterior chamber. Primary closure glaucoma is usually a bilateral disease. However, bilateral simultaneous acute attacks of acute angle closure glaucoma are rare.
3) Secondary glaucoma
Secondary glaucoma includes a variety of glaucomas which result from previous eye disease or trauma. This type of glaucoma may develop from uveitis, cataract, hyphema, complications from intraocular surgery, or long-term use of corticoid.
4) Infantile glaucoma
Infantile glaucoma is an inborn disability, this is caused by the blockage by abnormal tissue, resulting in inability in draining the aqueous from the anterior chamber. The symptoms include abnormally large eyes, unclear cornea and most of the infected babies have too much tear and are afraid of light. Although rare, infantile glaucoma is a worldwide problem. It requires early surgical treatment to prevent total blindness.
Common symptoms:
• lost or blurry side vision
• eye pain
• episodes of seeing floaters, spots or flashes of light
• frequent changes in eyeglass strength
• severe pain in the eye
• headache nausea
• partial loss of vision
Retinal Detachment
Retinal detachment occurs when the retina becomes separated from the back of the eye as a result of the spreading of a small tear. This can happen slowly over a period of weeks, or very suddenly, within only a few hours. Without appropriate treatments, patients may suffer from total blindness. Some eye injuries may cause retinal detachment. With age, the vitreous body will solidify and contract, and detach from the retina. If the detachment is sudden and vigorous, it will cause a tear in the retina, resulting in retinal detachment.
Small tears in the retina can be detected with the routine eye exams and treated with laser surgery to prevent further spreading. A detached retina can be reattached, but vision may be impaired or lost. Immediate treatment is crucial.
Retinal detachment can be classified into 2 types : primary and secondary, depending on the causes.
Symptoms:
• diminishing vision
• floating spots or specks and flashes of light
• disappearance of segments of the visual field
Causes:
• aging
• inherited
• myopia
• complications of eye surgery
• eye injuries
• can occur without any apparent cause or reason
Treatment: Surgical repair should be performed as soon as possible. Retinal detachment is considered a surgical emergency.
Uveitis
This is the inflammation of a part, or all of the uvea, or uvela tract. The uvea includes the choroid, ciliary body and iris of the eye. It occurs when microfilariae penetrate the sclera and enter the eyeball, and it is classified according to the anatomic location of the inflammation in the uveal tract. Nutrients that the eyeball need are transported by the vast vessel network in the uvea, that's why when the uvea is infected, other parts of the eye will also be affected. As the uvea covers the whole eyeball, uveitis is usually more severe than the other eye diseases.
Symptoms:
• light sensitive
• blurry vision
• severe pain in the eye
• severe redness of the eye
• diminishing vision
Causes:
• ocular contusion injury
• lens-induced uveitis
• arthritis
• it may occur with tuberculosis, leprosy, and lues
Treatment: Uveitis is usually managed with cycloplegics ( atropine ) and anti-inflammatory drugs ( corticosteroids ), either topical or subconjunctival, and frequent re-examination. Apart from medicine, the doctor may use laser or surgery.
Diabetic retinopathy / Diabetes mellitus
It is caused by diabetes, a group of disease in which the body is unable to regulate the amount of sugar ( glucose ) in the blood. Diabetes can affect the other organs and also the eye. The most serious eye problem associated with diabetes is retinopathy. This happens when the tiny blood vessels in the retina weaken or swell, causing blood leakage, new vessel formation and other changes that damage the nerve cells which transmit images to the brain. In the early stage, traces of blood and fat deposit will appear on the retina, but the patient's vision will be normal.
Diabetic retinopathy is a serious complication that often leads to visual impairment and is frequently complicated by cataract formation. In Hong Kong, the prevalence rate is estimated to be 8-10% of the population, it occurs in approximately 15%-30% of diabetic patients of less than 5 years history and 25%-50% of 5-15 years history. Microvascular damage from diabetes leads to micro-aneurysms, haemorrhage, exudates, and cotton-wool spots. Further progression if disease results in new vessel growth, or neovascularization which can cause haemorrage, scarring, and permanent visual loss. In the early stages, retinopathy can be treated by using laser therapy to seal leaking blood vessels.
Dry Eye
Tears, not only does it reflect one's emotion, it has its actual uses. Under normal conditions, the tear glands produce enough tears to moisturize the cornea and to avoid the evaporation of the eye surface. If the tear production is reduced, it will result in hot, dry, burning eyes.
Wet eye would seem to be the opposite of the dry eye, but in reality it is a reaction to the dry eye. When the eye is dry, it is stimulated and produce a lot of tears, therefore, wet eye may be a signal of dry eye.
The thin film of tears is critically important for maintaining the function and health of the cornea. Since the cornea doesn't have a direct blood supply, the surface cells must maintain metabolism by getting oxygen and nutrients, then getting rid of waste products by way of the tear supply.
The tear firm is made up of three layers:
1. The outer layer -- the lipid layer which acts as a lubricant so that the tear film is adhered to the eye and it prevents the aqueous layer from evaporating too rapidly.
2. The middle layer -- the watery, aqueous layer which supplies oxygen to the cornea.
3. The inner layer -- the mucin layer which controls the amount of water in contact with the cornea.
Tear gland function decreases with age. This produces a progressive drying of the conjunctiva with aging. For some of the patients, they may also have symptoms such as rheumatoid arthritis and dry mouth. These symptoms are called Sjogren's Syndrome. The dry eye may be treated with isotonic artificial tears. Closure of the lacimal puncti with thermal cautery can prevent drainage of tears and the increased tear film will moisten the ocular surfaces, improving dry eye symptoms.
Strabismus / Squint
Strabismus refers to the condition of the eyes being misaligned so that only one eye at a time fixes on the visual target. If left untreated, it will produce monocular visual disability or blindness.
Strabismus, the official term, can assume many forms:
1) Exotropia ('wall eyes') refers to outward deviation
2) Esotropia ('crossed eyes') refers to inward deviation
3) Hypertropia refers to upward deviation of one eye
4) Hypotropia refers to downward deviation of one eye
and even combinations such as out with down etc.
In all cases of strabismus, one eye does the sighting while the other eye looks somewhere else. In a few people the sighting eye and turning eye will alternate roles each periodically doing the sighting. A common misconception is that strabismus is caused by weak muscles. While on rare occasions a paralyzed or misconnected muscle is the culprit, the muscles attached to the eyeball are very strong and the range of movements quite remarkable. The real problem is that the two eyes just won't work jointly as the brain's passion to avoid double vision.
Another common type of strabismus is caused by high amounts of farsightedness. This is the classic case of one eye turning inward toward the nose. To see clearly, the farsighted eyes must use an exceptional amount of focusing power. But, since focusing and turning the eyes inward work together, double vision ensues. To get out of this quandary, the brain learned that by turning one eye inward a bit more, the image falls on the normal blind spot. Thus, only one image is seen. Other types of crossed eyes have other causes, yet are not know.
Some of the patients may have inherited strabismus. It occurs early in childhood without any apparent cause and is called Primary Strabismus. Another type of strabismus that follow trauma directly to one or both eyes is called Secondary Strabismus.
Secondary strabismus may be due to a cranial nerve palsy from:
• head injury
• intracranial mass ( brain tumor or abscess)
• vascular accident (stroke)
• diabetes mellitus
• vascular disease
• systemic hypertension
• heart disease
Strabismus cannot be treated solely by medication. The actual treatment procedures can be quite involved, but the following steps are taken:
1) Glasses are prescribed. If necessary, a prism effect is incorporated into the lenses to shift the images closer together
2) Vision therapy (orthoptics) is used to break up the suppression habit. Once there is an awareness of double vision when the eyes are not straight, the patient is trained to fuse the two images into one. As this progresses, the eyes will slowly assume a straight posture for longer periods of time.
3) Stereopsis is developed and the new vision pattern reinforced to keep the eyes from recrossing.
By ThinkQuest.org
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