View Full Version : blindness

24-07-2012, 11:14 AM
blindness: (tật) mù (cũng gọi là ablepsia; ablepsy)

blindness: the inability to see. This condition may be the result of disorders in the organs of sight or of damage or injury to certain areas of the brain

mù: không thể nhìn thấy. Tình trạng này có thể là do rối loạn cơ quan thị giác, hư hại hoặc tổn thương một số vùng ở não

24-07-2012, 11:18 AM
What is blindness?

Blindness is defined as the state of being sightless. A blind individual is unable to see. In a strict sense the word blindness denotes the condition of total blackness of vision with the inability of a person to distinguish darkness from bright light in either eye. The terms blind and blindness have been modified in our society to include a wide range of visual impairment. Blindness is frequently used today to describe severe visual decline in one or both eyes with maintenance of some residual vision.

Vision impairment, or low vision, means that even with eyeglasses, contact lenses, medicine or surgery, you don't see well. Vision impairment can range from mild to severe. Worldwide, between 300 million and 400 million people are visually impaired due to various causes. Of this group, approximately 50 million people are totally blind. Approximately 80% of blindness occurs in people over 50 years old

What are the different types of blindness?

Color blindness is the inability to perceive differences between some of the colors that others can distinguish. It is most often inherited (genetic) and affects about 8 % of males and under 1% of women. People who are color blind usually have normal vision otherwise and can function well visually. This is actually not true blindness.

Night blindness is a difficulty in seeing under situations of decreased illumination. It can be genetic or acquired. The majority of people who have night vision difficulties function well under normal lighting conditions. This is not a state of sightlessness.

Snow blindness is loss of vision after exposure of the eyes to large amounts of ultraviolet light. Snow blindness is usually temporary and is due to swelling of cells of the corneal surface. Even in the most severe of cases of snow blindness, the individual is still able to see shapes and movement.

People often say, "I am 'blind as a bat' without my glasses." All bat species have eyes, and most have excellent vision. More importantly, the term blindness means the inability to see despite wearing glasses. Anyone who has access to glasses and sees well with the glasses cannot be termed blind.


24-07-2012, 11:19 AM
What causes blindness?

The many causes of blindness differ according to the socioeconomic condition of the nation being studied. In developed nations, the leading causes of blindness include ocular complications of diabetes, macular degeneration, and traumatic injuries. In third-world nations where blindness is much more common and where about 85% of the world's blindness occurs, principal causes include infections, cataracts, glaucoma, injury, and inability to obtain any glasses.

Infectious causes in underdeveloped areas of the world include trachoma, onchocerciasis (river blindness), and leprosy. The most common infectious cause of blindness in developed nations is herpes simplex.

Other causes of blindness include vitamin A deficiency, retinopathy of prematurity, blood vessel disease involving the retina or optic nerve including stroke, ocular inflammatory disease, retinitis pigmentosa, primary or secondary malignancies of the eye, congenital abnormalities, hereditary diseases of the eye, and chemical poisoning from toxic agents such as methanol.

What are symptoms and signs of blindness?

All people who are blind or have visual impairment have the common symptom of difficulty seeing. People with similar levels of visual loss may have very different responses to that symptom. If one is born blind, there is much less adjustment to a non-seeing world than there is for people who lose their vision late in life, where there may be limited ability to cope with that visual loss. Support systems available to individuals and their psychological makeup will also modify the symptom of lack of sight. People who lose their vision suddenly, rather than over a period of years, also can have more problems from their visual loss.

Associated symptoms, such a discomfort in the eyes, awareness of the eyes, foreign body sensation, and pain in the eyes or discharge from the eyes may be present or absent, depending on the underlying cause of the blindness.

A blind person may have no visible signs of any abnormalities when sitting in a chair and resting. When blindness is a result of infection of the cornea (the dome in front of the eye), the normally transparent cornea may become white. This opaque cornea can make it difficult to view the colored part of the eye. In blindness from cataract, the normally black pupil may appear white. Depending on the degree of blindness, the affected individual will exhibit signs of visual loss when attempting to ambulate. Some blind people have learned to look directly at a source of conversation.


24-07-2012, 11:21 AM
How is blindness diagnosed?

Blindness is diagnosed by visual acuity testing in each eye individually and by measuring the visual field or peripheral vision. People may have blindness in one (unilateral blindness) or both eyes (bilateral blindness). Historical information regarding the blindness can be helpful in diagnosing the cause of blindness. Poor vision that is sudden in onset differs in potential causes than blindness that is progressive or chronic. Temporary blindness differs in cause from permanent blindness. The cause of blindness is made by examination of all parts of the eye by an ophthalmologist.

What are treatments for blindness?

The treatment of blindness depends on the cause of blindness. In third-world nations where there are many people who have poor vision as a result of a refractive error, merely prescribing and giving glasses will alleviate the problem. Nutritional causes of blindness can be addressed by dietary changes. There are hundreds of thousands of people who are blind from cataracts. In these patients, cataract surgery would, in most cases, restore their sight. Inflammatory and infectious causes of blindness can be treated with medication in the form of drops or pills.

What is the prognosis for blindness?

The prognosis for blindness again is dependent on its cause. In patients with blindness due to optic-nerve damage or a stroke of indeterminate age, visual acuity can usually not be restored. Patients with long-standing retinal detachment in general cannot be improved with surgical repair of their detachment. Patients who have corneal scarring or cataract have a good prognosis if they are able to access surgical care of their condition.


24-07-2012, 11:23 AM
When is someone considered legally blind?

Legal blindness is not a medical term. It is defined by lawmakers in nations or states in order to either limit allowable activities, such as driving, of individuals who are "legally blind" or to provide preferential governmental benefits to those people in the form of educational, service, or monetary assistance. Under the Aid to the Blind program in the Social Security Act passed in 1935, the United States Congress defined legal blindness as either central visual acuity of 20/200 or less in the better eye with corrective glasses or central visual acuity of more than 20/200 if there is a visual field defect in which the peripheral field is contracted to such an extent that the widest diameter of the visual field subtends an angular distance no greater than 20 degrees in the better eye.

It is estimated that approximately 700,000 people in the United States meet the legal definition of blindness.

Is blindness preventable?

Between 80%-90% of the blindness in the world is preventable through a combination of education and access to good medical care. Most traumatic causes of blindness can be prevented through instruction in eye protection. Nutritional causes of blindness are preventable through proper diet. Most cases of blindness from glaucoma are preventable through early detection and appropriate treatment. Visual impairment and blindness caused by infectious diseases have been greatly reduced through international public-health measures.

The majority of blindness from diabetic retinopathy is preventable through careful control of blood-sugar levels, exercise, avoidance of obesity and smoking, and emphasis on eating foods that do not increase the sugar load (complex, rather than simple carbohydrates). There has been an increase in the number of people who are blind or visually impaired from conditions that are a result of living longer. As the world's population achieves greater longevity, there will also be more blindness from other diseases such as macular degeneration. There are, however, new and evolving treatments for this disease and for diabetic retinopathy. Regular eye examinations may often uncover a potentially blinding illness which can then be treated before there is any visual loss.

Patients who have untreatable blindness require reorganization of their habits and reeducation to allow them to do everyday tasks in different ways. Visual aids, text-reading software, and Braille books are available, together with many simple and complex devices to provide functional improvement for the individual with blindness or low vision. In the United States and most other developed nations, financial assistance through various agencies can pay for the training and support necessary to allow a blind person to function.

John Milton and Helen Keller are well known for their accomplishments in life despite being blind. There are countless other unnamed individuals with blindness, however, who, despite significant visual handicaps, have had full lives and enriched the lives of those who have had contact with them.

Last Editorial Review: 3/10/2010 3:30:02 PM


24-07-2012, 11:28 AM
Leading Causes of Blindness


Cataracts are a clouding of the lenses in your eyes. They affect vision and are very common in older people. More than 22 million Americans have cataracts. They are the leading cause of blindness in the world. By age 80, more than half of all people in the United States either will have a cataract or have had cataract surgery.
Common symptoms are:

Blurry vision

Colors that seem faded


Not being able to see well at night

Double vision

Frequent prescription changes in your eye wear

Treatment with new glasses, brighter lighting, anti-glare sunglasses, or magnifying lenses can help at first. Surgery is also an option. It involves removing the cloudy lens and replacing it with an artificial lens. Wearing sunglasses and a hat with a brim to block ultraviolet sunlight may help to delay cataracts.


Photo courtesy of National Eye Institute, NIH


Glaucoma damages the eye's optic nerve and is a leading cause of blindness. It usually happens when the fluid pressure inside the eyes slowly rises, damaging the optic nerve. Often there are no symptoms at first, but a comprehensive eye exam can detect it. About 2.3 million Americans suffer from glaucoma. It is estimated that an additional 2 million have the disease but don't know it.

Glaucoma is a leading cause of blindness among African Americans and Hispanics. African Americans experience glaucoma at a rate three times that of whites. They suffer blindness four times more frequently. Between the ages of 45 and 64, glaucoma is 15 times more likely to cause blindness in African Americans than in whites.

People at risk should get eye exams at least every two years, especially:

African Americans over age 40

People over age 60, especially Hispanics

People with a family history of glaucoma

Treatment usually includes prescription eye drops and/or surgery. There is no "cure" for glaucoma. Early diagnosis and treatment can control glaucoma before vision loss or blindness occurs. New research is focusing not only on lowering pressure inside the eye, but also exploring medications to protect and preserve the optic nerve from the damage that causes vision loss. There has been progress in understanding the genetics of glaucoma in the last few years, including the discovery of genes found to be associated with many forms of glaucoma.


Age-Related Macular Degeneration.
Photo courtesy of National Eye Institute, NIH

Macular degeneration

Macular degeneration, often called age-related macular degeneration (AMD), is a leading cause of vision loss in Americans 60 and older. It is a disease that destroys the sharp, central vision needed to see objects clearly. This affects the ability to read, drive, watch television, and do routine daily tasks.

AMD affects the macula, the part of the eye that allows you to see fine detail. It does not hurt, but causes cells in the macula to die. In some cases, AMD advances so slowly that people notice little change in vision. In others, the disease progresses faster and may lead to vision loss in both eyes. There are two kinds of AMD—wet and dry. Wet AMD occurs when abnormal blood vessels behind the retina start to grow under the macula. Dry AMD occurs when the light-sensitive cells in the macula slowly break down, gradually blurring central vision in the affected eye.

Treatment: Although there is no cure for AMD at this time, regular eye exams can detect the disease so treatment can be most effective. Findings from the NEI-supported Age-Related Eye Disease Study (AREDS) show that a specific combination of vitamins and minerals can help slow the progression of advanced AMD. Treatments for wet AMD include laser surgery, photodynamic therapy, and drugs injected into the eye. The NEI recently started a clinical trial to compare the relative safety and effectiveness of two drugs currently used to treat wet AMD. The two drugs, which are injected into the eye, are Lucentis (ranibizumab) and Avastin (bevacizumab). NEI is also supporting AREDS2 to learn whether a modified combination of vitamins and minerals can further help people with AMD.

Diabetic Retinopathy

Diabetic retinopathy is caused by diabetes. It affects the retina, the light-sensitive tissue at the back of the eye, and causes the most blindness in U.S. adults. It affects the vision of more than half of the 18 million people diagnosed with diabetes age 18 or older.

People with diabetes should have a complete eye exam through dilated pupils at least once a year.

Treatment: Diabetic retinopathy is treated with surgery or laser surgery. With timely treatment; adequate control of blood sugar, blood pressure, and cholesterol levels; and regular follow up, 90 percent of all cases of blindness from diabetes can be prevented.