Blindness is defined as the state of being sightless. A blind individual is unable to see. In the strictest sense, the word blindness denotes the condition of total blackness of vision including a person’s inability to distinguish darkness from bright light in either eye. The terms “blind” and “blindness” have been modified to include a wide range of visual impairment. Today, the term “blindness” is frequently used to describe severe visual decline in one or both eyes, with some residual vision maintained. Vision impairment, or low vision, means that even with eyeglasses, contact lenses, medicine or surgery, an individual doesn’t see well. Vision impairment can range from mild to severe. Between 300 million and 400 million people worldwide are visually impaired due to various factors. Of this group, approximately 50 million people are totally blind. Approximately 80% of blindness occurs in people over 50 years old.
The picture on the left depicts normal vision. The next page depicts the effects of disease on vision. Imagine the millions of people worldwide who are living daily with such impaired vision or total blindness.
Blindness and low vision
285 million people around the world are visually impaired; 40 million are blind and 246 million suffer from low vision. Global estimates show that, without intervention, the number of blind individuals will increase to 76 million by the year 2020. This represents one of the most serious health issues facing the world today. Blindness affects not only individuals and their families, but whole communities as well. Fortunately, there is good news – 80 percent of blindness in the developing world can be successfully treated or prevented.
Glaucoma is an eye disease in which the optic nerve is damaged in a characteristic pattern. Glaucoma is the leading cause of blindness throughout the world. It can permanently damage vision in the affected eye(s) and lead to blindness if left untreated. Individuals over 40 who are currently living with glaucoma might not even be aware they have it, as symptoms may not be present.
A cataract manifests as clouding in the eye. It develops in the crystalline lens or in its envelope, also called the lens capsule. The lens is located near the front of the eye and focuses on the retina, at the back of the eye, to form the image we see. A cataract may cloud the entire lens, or affect just a small part. Cataracts vary in degree from slight to complete opacity and obstruct the passage of light. Age-related cataracts are responsible for 48% of world blindness, which represents about 18 million people. When developed in an elderly individual, the cataract is known as a “senile cataract”, whereas, in children, it is called a “congenital cataract”.
Macular degeneration is a medical condition which usually affects older adults. It results in a loss of vision in the macula and damage to the retina. It is a major cause of blindness and visual impairment in older adults. The macula is the central area of the retina, which provides the most detailed central vision. This term generally refers to Age-related macular degeneration (AMD or ARMD).
Diabetic retinopathy is caused by complications related to diabetes, which can eventually lead to blindness. It is an ocular manifestation of systemic disease which affects up to 80% of all patients who have had diabetes for 10 years or more. Diabetic retinopathy is the result of microvascular retinal changes. It usually affects both eyes. People who have diabetic retinopathy often don’t notice changes in their vision in the disease’s early stages. But, as it progresses, diabetic retinopathy usually causes vision loss that, in many cases, cannot be reversed.
A refractive error, or refraction error, is an error in the eye’s ability to focus on light. It is a common factor in the reduction of visual acuity. An eye that is affected by refractive error is said to have ametropia, or be ametropic, when viewing distant objects. The word “ametropia” can be used interchangeably with “refractive error” or “image formation defects”. The diagnosis of a refractive error is usually confirmed by an eye care professional during an examination using an instrument called a phoropter.
Trachoma is the world’s leading cause of preventable blindness. Caused by a bacterial infection, trachoma spreads easily through contact with eye discharge from infected people on hands, towels and clothing, as well as through direct transmission by flies.
Onchocerciasis is often called “river blindness”. It occurs in central Africa and Central America near flowing rivers and streams, where the species of black flies that transmits the disease is most often found. Bacteria from the flies allow parasitic worms to enter a person’s bloodstream, where the worms can live up to 14 years. Symptoms of river blindness often show up 1 to 3 months after infection.
Data collected from various sources presents the most up-to-date information on childhood blindness, and suggests that 5% of worldwide blindness involves children younger than 15 years of age. In developing countries, 50% of the population falls within this age group. Using the World Health Organization’s criteria, there are over 3.0 million children worldwide who are blind.