The Basics of Permanent Visual Loss

The basics of permanent visual loss.

By Terry Loerch

Blindness is defined as the condition of being sightless in both eyes or in other words  “blindness” defines the inability of a person to distinguish darkness from bright light in either eye.  A blind individual is not able to see. The terms blind and blindness have been adjusted in our society and consists of a wide range of visual declines. Blindness is frequently used today to describe severe visual impairments in one or both eyes with the maintenance of some residual vision.

Vision impairment, or low vision, means that it cannot be corrected with eyeglasses, contact lenses, medicine, or surgery and the individual cannot see well. Vision impairment can differ from mild to severe forms. All around the world, between 300 million-400 million individuals have visual impairment due to different causes and factors, and of this group, about 50 million people are completely blind. In 80% of the cases, blindness happens in people over 50 years of age.

When is someone called legally blind?

According to the Aid to the Blind program in the Social Security Act passed in 1935, the United States Congress has constructed and determined legal blindness as either central visual perception of 20/200 or less in the better eye with corrective eyeglasses or central visual perception of more than 20/200 if there is a visual field defect in which the peripheral visual field is contracted to such a degree that the widest diameter of the visual field links to a bifurcated distance is no greater than 20 degrees in the better eye. On the other hand, blindness in one eye is never defined as legal blindness if the other eye is normal or near-normal sightseeing.

It is estimated that more than 1 million people in the United States meet the criteria to be categorized under the legal definition of blindness.

What are the different categories and types of blindness?

Color blindness is the failure to perceive differences in various shades of colors, specifically green and red, that others can distinguish. It is most often genetically inherited and it affects about 8% of males and under 1% of women. Individuals who are color blind usually have normal sight and can function well visually and this is actually not true blindness.

Night blindness makes it difficult in seeing under environments of decreased light. It can be genetic or attained during life. The majority of people who have night vision problems function well under normal lighting situations; this is not a state of blindness.

Snow blindness is a loss of vision after being exposed to large amounts of ultraviolet light. Snow blindness is usually temporary and is because of the swelling of cells of the corneal surface. Even in the most severe forms of snow blindness, the individual is still capable of seeing shapes and movement.

What leads to blindness?

The many causes of blindness vary according to the socio-economic conditions of different nations. In developed nations, the main causes of blindness consist of ocular complications of diabetes, macular degeneration, glaucoma, and traumatic injuries. In third-world nations where 90% of the world’s visually damaged population lives, the leading causes are infections, cataracts, glaucoma, injury, and lack of access to any glasses.

Infectious causes in underdeveloped countries of the world involve trachoma, onchocerciasis (river blindness), and leprosy. The most usual infectious cause of blindness in developed nations is herpes simplex, while other causes of blindness include vitamin A deficiency, retinopathy of prematurity, blood vessel diseases affecting the retina or optic nerve including stroke, infectious diseases of the cornea or retina, ocular inflammatory disease, retinitis pigmentosa, primary or secondary malignancies of the eye, congenital abnormalities, genetic diseases of the eye, and chemical intoxications from agents such as methanol.

What puts you at risk for blindness?

A leading risk factor for blindness is living in a third-world country without access to proper medical care. Other risk factors include poor prenatal care, premature birth, advancing age, poor nutrition, not wearing safety glasses when needed, lack of good hygiene, tobacco use, a family history of blindness, the presence of different ocular diseases and the existence of medical pathologies including diabetes mellitus, high blood pressure, cerebrovascular and cardiovascular disease.

What are the signs and symptoms of visual loss?

All individuals who are blind or have visual loss have the mutual symptom of difficulty seeing and they may have very different reactions to that symptom. If one is born blind, there is much less adaptation to a non-seeing world than there is for people who lose their vision late in adult life, where there may be only a small extent to cope with that visual loss. Support systems available to people and their psychological responses will also adjust the symptom of lack of sight. For people who lose their vision abruptly, rather than over a long period of time, it can be more challenging to adjust to their visual loss.

Common symptoms, such as discomfort, awareness of the eyes, foreign body sensation, and pain or discharge from the eyes may be present or absent, depending on the bottom cause of the visual loss.

A blind person may not present any visible signs of any anomalies when sitting in a chair and resting. However, when blindness results from infection of the cornea (the dome in front of the eye), the normally transparent cornea may have a color of white or gray, making it difficult to distinguish the colored part of the eye. In blindness from cataract, the normally black pupil might present white. Depending on the level of blindness, the affected individual will show signs of visual impairment when trying to ambulate. Some blind people have learned to look directly at the person they are talking with, which makes it less obvious that they are blind.

How is blindness diagnosed?

Blindness is diagnosed by testing each eye alone and by assessing the visual acuity and the visual field, or peripheral vision. People might have a visual loss in one (unilateral blindness) or both eyes (bilateral blindness). Obtaining information regarding blindness can be helpful in finding the cause of blindness. Poor vision that is sudden in onset alters in potential causes than blindness that is progressive over a long period of time. Temporary blindness also varies in cause from permanent blindness. The cause of blindness is diagnosed by a thorough medical examination by an ophthalmologist.

How can it be treated?

The treatment of visual loss or blindness depends on the cause. In third-world countries where many people have poor vision because of a refractive error, barely prescribing and giving glasses will enhance the problem. Nutritional causes of visual impairment can be addressed by dietary adjustments. There are millions of people worldwide who go blind from cataracts. In these patients, cataract removal surgery would, in most cases, restore their vision. Inflammatory and infectious causes of blindness can be treated with medication available in the form of eye drops or pills. Corneal transplantation may help people whose vision is lacking as a result of corneal injury.

What is the long-term prognosis?

The prognosis for blindness depends on its cause. In patients with blindness due to optic nerve damage (glaucoma) or a completed stroke, visual acuity cannot be restored in most cases. The same scenario goes for patients with long-standing retinal detachment, generally cannot be improved with surgical repair of their detachment. Patients who have corneal injuries or cataracts usually have a good prognosis if they are able to access surgical treatment of their condition.

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