BLINDNESS

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 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, someone doesn't see well. Vision impairment can range from mild to severe. Worldwide, between 300 million-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 of age.

What causes color blindness?

Most color vision problems are inherited (genetic) and are present at birth.

People usually have three types of cone cells in the eye. Each type senses either red, green, or blue light. You see color when your cone cells sense different amounts of these three basic colors. The highest concentration of cone cells are found in the macula, which is the central part of the retina 

Inherited color blindness happens when you don't have one of these types of cone cells or they don't work right. You may not see one of these three basic colors, or you may see a different shade of that color or a different color. This type of color vision problem doesn't change over time.

A color vision problem isn't always inherited. In some cases, a person can have an acquired color vision problem. This can be caused by:

• Aging.
• Eye problems, such as glaucoma, macular degeneration, cataracts, ordiabetic retinopathy.
• Injury to the eye.
• Side effects of some medicines.

What are the symptoms?

The symptoms of color vision problems vary:

• You may be able to see some colors but not others. For instance, you may not be able to tell the difference between some reds and greens but can see blue and yellow easily.
• You may see many colors, so you may not know that you see color differently from others.
• You may only be able to see a few shades of color, while most people can see thousands of colors.
• In rare cases, some people see only black, white, and gray.

How is color blindness diagnosed?

Tests measure how well you recognize different colors.

• In one type of test, you look at sets of colored dots and try to find a pattern in them, such as a letter or number. The patterns you see help your doctor know which colors you have trouble with.
• In another type of test, you arrange colored chips in order according to how similar the colors are. People with color vision problems cannot arrange the colored chips correctly.

Because a color vision problem can have a big impact on a person's life, it is important to detect the problem as early as possible. In children, color vision problems can affect learning abilities and reading development. And color vision problems may limit career choices that require you to tell colors apart. Most experts recommend eye exams for children between ages 3 and 5. Vision screening is recommended for all children at least once before entering school, preferably between the ages of 3 and 4.

How is it treated?

Inherited color vision problems cannot be treated or corrected.

For the most common type of color blindness—red-green color deficiency—no treatment is needed, because you function normally. You may not be aware that you do not see colors the way they are seen by others.

Some acquired color vision problems can be treated, depending on the cause. For example, if a cataract is causing a problem with color vision, surgery to remove the cataract may restore normal color vision.

You can find ways to help make up for a color vision problem, such as:

• Wearing colored contact lenses. These may help you see differences between colors. But these lenses don't provide normal color vision and can distort objects.
• Wearing glasses that block glare. People with severe color vision problems can see differences between colors better when there is less glare and brightness.
• Learning to look for cues like brightness or location, rather than colors. For example, you can learn the order of the three colored lights on a traffic signal.

How can you help a child who has color blindness?

Color vision problems may make it harder for children to learn and read, which can lead to poor schoolwork and low self-esteem.

You can help your child these ways.

• Make sure your child is tested for color vision problems during routine eye tests. The sooner you know there is a problem, the sooner you can help your child. Eye exams should be done at all well-child visits.1
• Tell your child's teachers and other school staff about the problem. This may be helpful. Suggest seating your child where there is no glare and using a color of chalk that your child can see.

What are the different types of blindness?

Color blindness is the inability to perceive differences in various shades of colors, particularly green and red, 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.

What causes blindness?

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.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 90% of the world's visually impaired population lives, the principal causes are infections, cataracts, glaucoma, injury, and inability to obtain any glasses.

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 difficulty adjusting to 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. However, when blindness is a result of infection of the cornea (the dome in front of the eye), the normally transparent cornea may become white, making 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 the person they are speaking with, so it is not obvious they are blind.

How is blindness diagnosed?

Blindness is diagnosed by testing each eye individually and by measuring the visual acuity and 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 a thorough examination by an ophthalmologist.

What are treatments for blindness?

What is the prognosis for blindness?The treatment of visual impairment or blindness depends on the cause. In third-world nations where many people 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.

The prognosis for blindness, again, is dependent on its cause. In patients with blindness due to optic-nerve damage or a stroke, 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.

Is blindness preventable?

Blindness is preventable through a combination of education and access to good medical care. Most traumatic causes of blindness can be prevented through 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. However, these diseases are so common that research and treatment are constantly evolving. Regular eye examinations may often uncover a potentially blinding illness that can then be treated before there is any visual loss.

There is ongoing research regarding gene therapy for certain patients with inheritable diseases such as Leber's congenital amaurosis (LCA) and retinitis pigmentosa.

Patients who have untreatable blindness need tools and help to reorganize their habits and the way in which they perform their everyday tasks. Organizations, such as the Braille Institute, offer helpful resources and support for people with blindness and for their families. Visual aids, text-reading software, and Braille books are available, together with many simple and complex technologies to assist them in functioning more effectively. 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.