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. Blindness is strictly defined as the state of being totally sightless in both eyes. A completely blind individual is unable to see at all. The word blindness, however, is commonly used as a relative term to signify visual impairment, or low vision, meaning that even with eyeglasses, contact lenses, medicine or surgery, a person does not see well. Vision impairment can range from mild to severe.

A person is legally blind if his/her central visual acuity, that is (what they see in front of them), is less than 20/200 in their good eye after correction, such as glasses or contacts. 20/200 visual acuity means that a person can see at 20 feet what a person with 20/20 vision can at 200 feet. A person can also be considered legally blind if their visual field, that is what they perceive to either side of them is 20 degrees or less.

When a person is considered legally blind?

Legally blind is defined as “central visual acuity 20/200 or less in the better eye with best correction or widest diameter of visual field subtending an angle of no greater than 20 degrees”. This simply means that even with corrective lenses or surgery you would have to be 20’ or closer to an object than someone with normal vision.

In the United States, any person with vision that cannot be corrected to better than 20/200 in the best eye, or who has 20 degrees or less of visual field remaining, is considered legally blind. This term was established to define the level of visual impairment that has been defined by law either to limit driving activities for safety reasons or to determine eligibility for government-funded disability benefits.

When is a person classified as blind?

In most cases, this term is used for those that have complete or nearly complete vision loss. However, most people that are classified as “blind” have some remaining sight—a small percentage of people are totally without sight. Blindness and legal blindness are often used interchangeably.


Economic blindness: Inability of a person to count fingers from a distance of 6 meters or 20 feet technical Definition

Social blindness: Vision 3/60 or diminution of field of vision to 10°

Manifest blindness: Vision 1/60 to just perception of light

Absolute blindness: No perception of light

Curable blindness: That stage of blindness where the damage is reversible by prompt management e.g. cataract

Preventable blindness: The loss of blindness that could have been completely prevented by institution of effective preventive or prophylactic measures e.g. xerophthalmia, trachoma and glaucoma 

Avoidable blindness: The sum total of preventable or curable blindness is often referred to as avoidable blindness.


Globally, the leading causes of vision impairment are:

Cataract: Cataracts occur when the normally crystal clear lens of the eye becomes cloudy. This causes blurry vision, faded colors, and problems seeing through glare. This means that the light that comes through the pupil and passes through the lens to be focused to the retina is blurred. This will cause your vision to become cloudy, blurry and, or, dim. Colors may not seem as bright or vivid as before. It’s like looking through the dirty windshield of a car. This condition occurs gradually and you may not notice it at first. Cataracts can be treated with surgery.

Risk Factors—Cataracts

• Increasing age, especially over age 50 • Prolonged exposure to ultraviolet B (UV-B) light, especially in latitudes closer to the equator • Diabetes mellitus • Cigarette smoking • Alcohol use • Diet low in antioxidants, especially vitamins E and B • High blood pressure • Eye injury/surgery • Steroid use • Female gender

Age-related macular degeneration: Commonly referred to as AMD, age-related macular degeneration is the leading cause of impairment of reading and close-up vision among people over 65. AMD results in damage to one’s central vision, which is needed for common daily tasks such as reading and driving. Macular Degeneration destroys the light sensitive cells in the macula, the part of the eye that lets you see objects in great detail. Often, the progress of AMD is so slow that you do not notice any change in your vision, but it can progress quickly as well. There are two types of Macular Degeneration: wet and dry. Wet Macular Degeneration occurs when irregular blood vessels begin growing behind the retina under the macula. Dry Macular Degeneration is caused by the breakdown of light sensitive cells in the macula causing the central vision to blur. The treatment for Wet Macular Degeneration includes surgery. At this time, no treatment exists for Dry Macular Degeneration.

Risk Factors—Macular Degeneration

• Age (25% of those 65–74 and 33% of those over 74 years) • Cigarette smoking • Female gender and early menopause • High blood pressure or cardiovascular disease • Diet high in mono- or polyunsaturated fats, or linoleic vegetable fats, especially those found in snack foods • Prolonged sun exposure

Glaucoma: Legal blindness can also be caused by glaucoma, a disease in which the retinal neurons that send the signal from the eye to the brain die. This disease most often progresses slowly over time, with patients losing part of their visual field and/or visual acuity. If the visual field diminishes to 20 degrees or less, then the patient is legally blind. The normal binocular visual field (using both eyes) in the horizontal plane is about 180 degrees. Glaucoma is a disease that damages your eye’s optic nerve. It is caused by excess fluid in the eye which increases the eye pressure. This fluid is called aqueous humor. It is produced in the front portion of the eye and leaves the eye through the drainage angle. This keeps the intraocular pressure, at a healthy level. This pressure may vary from person to person. When the fluid does not leave the eye correctly, it will cause pressure to increase which will gradually damage the optic nerve.

There are several types of glaucoma. The two most common forms being: Primary Open-angle Glaucoma and Normal-tension Glaucoma. Open-angle Glaucoma is the most prevalent and happens when your eye can no longer drain fluid efficiently, causing the pressure to build. Open-angle Glaucoma has no early symptoms. As it progresses the optic nerve will become damaged, and you will start to notice blank spots in your field of vision. These spots will grow larger until all optic nerves are damaged, at which point, you will be blind.

Normal Tension Glaucoma is characterized by low pressure in the eye. This type of Glaucoma can also cause nerve damage and loss of vision. Treatment for both Open-angle Glaucoma and Normal tension Glaucoma is the same. The disease can be managed by prescription eye drops or surgery.

Unlike Primary Open-angle Glaucoma however, Primary Acute Closed-angle Glaucoma happens quite suddenly and should be attended to immediately. It results from a buildup of fluid because the drainage system is blocked and fluid can no longer drain from the eye.

Risk Factors—Glaucoma

• Increased intraocular pressure (IOP) • Age, usually over age 40 • Family history (genetics or similar environment) • Race or ethnicity: African ancestry (increased IOP; develops at earlier age) • Race or ethnicity: Caucasian of northern Europe ancestry (pseudoexfoliative type) • Race or ethnicity: Asian (angle closure type) • Arteriosclerosis • Near or far sightedness (each predisposes to different type)

Diabetic retinopathy: Commonly referred to as DR, typically occurs in four stages and is characterized by progressive damage to the blood vessels of the retina. Diabetic retinopathy is a common side effect of diabetes. Diabetic retinopathy occurs when the systemic damage caused by diabetes begins to affect the retina. Specifically, the blood vessels that nourish the retina can be negatively affected by diabetes, causing vision loss through bleeding and damage to the retina.

Diabetic Retinopathy is caused by diabetes. It affects the retina, the part of the eye sensitive to light. It is a result of high blood glucose, or sugar, over a prolonged period of time. High blood sugar prevents the blood vessels in the back of the eye from delivering the proper nutrients to the retina. Early on in the progress of the disease, these blood vessels will leak fluid and will cause site distortions. As the disease progresses, new blood vessels are formed around the retina and in the vitreous humor. These blood vessels will bleed making the vision cloudy and eventually causing the retina to detach. If not treated, a retinal detachment may cause permanent blindness. Vision loss caused by Diabetic Retinopathy can be prevented by laser surgery, a proper diet and controlling your blood glucose levels and blood pressure.

Trachoma: Repeated infections with the bacteria Chlamydia trachomatis cause the inside of the eyelid to scar, turn inward and painfully scratch the cornea, eventually leading to irreversible blindness. In its earlier stages, trachoma is treated with antibiotics and is preventable through improved hygiene and sanitation. In the final stage of the illness, referred to as Trachomatous Trichiasis, surgery on the eyelid is the only way to prevent the loss of sight.

Retinitis Pigmentosa: Retinitis Pigmentosa affects the retina’s ability to respond to light. It is a geneticly inherited disease. The symptoms include loss of night vision and peripheral vision. The gradual degeneration of the retina’s Photoreceptor cells (rods and cones) will eventually cause the individual to become blind As the disease progresses. For example, retinitis pigmentosa can cause “tunnel vision,” in which only a tiny window of central vision remains. Such patients might be able to read 20/20 size letters, but would be legally blind because of the small visual field. 

River blindness (onchocerciasis): is a parasitic disease which causes inflammation and bleeding that leads ultimately to blindness and other disabling effects. 

There is some variation in the causes across countries. For example, the proportion of vision impairment attributable to cataract is higher in low- and middle-income countries than high-income countries. In high income countries, diseases such as diabetic retinopathy, glaucoma and age-related macular degeneration are more common.

Among children, the causes of vision impairment vary considerably across countries. For example, in low-income countries congenital cataract is a leading cause, whereas in high income countries it is more likely to be retinopathy of prematurity.


If you’re completely blind, you see nothing. If you’re partially blind, you might experience the following symptoms:

Symptoms of blindness in infants

Your child’s visual system begins to develop in the womb. It doesn’t fully form until about 2 years of age.

By 6 to 8 weeks of age, your baby should be able to fix their gaze on an object and follow its movement. By 4 months of age, their eyes should be properly aligned and not turned inward or outward.

The symptoms of visual impairment in young children can include:


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 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. Improvements in diagnosis and prevention of retinopathy of prematurity, a potentially blinding illness seen in premature babies, have made it an avoidable cause of blindness today.


A principal risk factor for blindness is living in a third-world nation without ready access to modern medical care. Other risk factors include poor prenatal care, premature birth, advancing age, poor nutrition, failing to wear safety glasses when indicated, poor hygiene, smoking, a family history of blindness, the presence of various ocular diseases and the existence of medical conditions including diabetes mellitus, hypertension, cerebrovascular disease, and cardiovascular disease.


Over the last few years, WHO has developed and implemented several tools to support countries to assess the provision of eye care services:

Anyone who meets one of the following criteria is eligible to receive a Certificate of Blindness/Visual Impairment:

·       Total blindness

·       Visual acuity which is less than 3/60 in the better eye, even with the assistance of eyeglasses

·       Field of vision which is less than 20° in the better eye, even with the assistance of eyeglasses

WHO also developed and launched the World report on vision. The report offers recommendations, including a number focused on ensuring comprehensive and integrated eye care in countries. It is expected that by shaping the global agenda on vision, the report will assist Member States and their partners in their efforts to reduce the burden of eye conditions and vision impairment and achieve the Sustainable Development Goals (SDGs), particularly SDG target 3.8 on universal health coverage.

Ophthalmology is the specialty of medicine that deals with diagnosis and medical and surgical treatment of eye disease. Therefore, ophthalmologists are the specialists who have the knowledge and tools to diagnose the cause of blindness and to provide treatment, if possible.

To get a disability certificate for blindness, contact your nearest government hospital and get yourself evaluated. The doctors assess the extent of vision loss and a certificate is given accordingly.

The medical authority shall comprise of one ophthalmologist and certificate of disability shall be countersigned by Medical Superintendent or Chief Medical Officer or Civil Surgeon or any other equivalent authority as notified the State Government.

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 interacted with them.