Blindness

What is Blindness?

When we discuss total blindness, low vision, and visual impairment, we’re talking about a range of conditions that affect vision in different ways and can significantly impact a person’s daily life.

In simple terms, total blindness means a person can’t see anything at all, including light. Thankfully, this condition is rare and only affects about 15% of people with serious eye disorders.

Low vision is a term used for those who can’t see clearly, and this problem can’t be fully resolved with glasses, contact lenses, medicine, surgery, or devices to assist vision.

Visual impairment means a person’s ability to see is decreased to an extent that it interferes with their daily activities, like reading, driving, or watching TV. This term is different from others because it refers to how vision loss affects day-to-day living rather than its impact on certain measurements of vision such as visual acuity (sharpness) or visual field (range you can see)

Common symptoms of visual impairment can be:

• Blurred vision
• Seeing hazy or cloudy images
• Having wavy spots in your central vision
• Poor peripheral vision (i.e., not being able to see well to the side when looking straight ahead)
• Difficulty in seeing at night
• Problems with distinguishing colors

The term “legal blindness” is used by the US Social Security Administration to classify people who qualify for certain benefits like disability, tax exemptions, and vocational training. Legal blindness is defined as having either a visual acuity of 20/200 or worse in your better-seeing eye, even with correction like glasses, or having a visual field where you can’t see beyond 20 degrees in your better-seeing eye.

To determine visual acuity or field, various tests are used. Distance visual acuity is usually tested using a method similar to the Snellen chart (a chart with lines of letters decreasing in size). Nowadays, there are also modern low-vision test charts. According to the updated rules, if a person cannot read at least one letter on the 20/100 line, he or she is classified as legally blind.

Other types of tests for the visual field, like automated perimetry (measures your peripheral vision), are also used. Basic screening tests are not accepted as legitimate measures of legal blindness.

The World Health Organization (WHO) has a classification system for visual impairment based on visual acuity and field measurements:

• Normal vision: 20/10-20/25
• Near-normal vision impairment: 20/30-20/60
• Moderate vision impairment: 20/70-20/160
• Severe vision impairment: 20/200-20/400 or a visual field of 11-20 degrees
• Profound vision impairment: 20/500-20/1000 or a visual field of 6-10 degrees
• Near-total vision impairment: Ability to only detect hand movements, light or a visual field of 5 degrees or less
• Total vision impairment: No ability to perceive light

WHO also has a definition for blindness, which essentially means the inability to see anything clearer than 3/60 (as per Snellen’s chart) or its equivalent. In situations where there’s no visual acuity chart, if a person can’t count fingers from a distance of 3 meters in daylight, that’s considered equivalent to 3/60.

Finally, in line with WHO’s categorization, the National Programme on Control of Blindness (NPCB) also classify levels of visual impairment based on maximum and minimum visual acuity limits starting from low vision to absolute blindness. This helps in standardized assessments of visual loss across various eye conditions.

What Causes Blindness?

There are many conditions that can cause blindness. The main conditions include cataracts, age-related macular degeneration, glaucoma, diabetic retinopathy, and trachoma.

Cataracts make the lens of your eye yellow and hard and it’s the top cause of blindness in both developing and developed countries worldwide.

Age-related macular degeneration damages a part of your eye called the retina, particularly a section called the macula. This is the most common cause of blindness in Caucasians and people who are 65 or older.

Glaucoma damages the optic nerve, which is the part that carries images from your eye to your brain. This condition is the leading cause of blindness in African Americans.

A condition called diabetic retinopathy that happens when someone has systemic diabetes, is the chief cause of new cases of blindness in adults between the ages of 25 and 64.

Trachoma is a condition caused by the bacteria ‘Chlamydia trachomatis’. The number of cases is going down because of public health actions.

A high number of people have reduced vision because of an easily repairable problem called uncorrected refractive error, which is when the shape of your eye doesn’t bend light correctly. This condition can usually be easily fixed or ‘cured’ with proper vision correction.

It’s estimated that about 90% of people who are visually impaired live in developing countries or low-income situations. Roughly 80% of all visual impairments worldwide could be prevented, treated, or cured with suitable eye care.

The most frequent reasons of blindness are:

Cataracts (51%)
Glaucoma (8%)
Age-Related Macular Degeneration (5%)
Corneal Opacification, or clouding of the cornea (4%)
Childhood blindness (4%)
Refractive errors (3%)
Trachoma (3%)
Diabetic Retinopathy (1%)
Undetermined (21%)

In more developed countries, the main causes of blindness are:

Injury
Glaucoma
Diabetic Retinopathy
Vascular Occlusions – lack of blood flow
Cataract
Age-Related Macular Degeneration

In children, the leading causes of blindness are:

Xerophthalmia – dryness in the eyes
Congenital Glaucoma – glaucoma present at birth
Congenital Cataract – cataract present at birth
Optic Atrophy – damage to the optic nerve
Injury
Amblyopia, or lazy eye
Refractive errors
Trachoma

Risk Factors and Frequency for Blindness

The World Health Organization (WHO) estimates that around 285 million people have some sort of visual impairment. This includes 39 million who are completely blind and 246 million who have poor vision. The majority of people with blindness, around 90%, live in developing countries. For every person who is blind, there’s an average of 3.4 people with low vision. However, this ratio varies from country to country, going from 2.4 to 5.5 people.

An additional report shows that worldwide, 180 million people have visual disabilities, and out of these, 45 million are blind. Shockingly, about 80% of these cases of blindness could have been prevented.

Most blind people, around 82%, are 50 years of age or older. But childhood blindness is also a serious issue, with an estimated 1.4 million blind children under the age of 15. Additionally, females are statistically more likely to be visually impaired than males.

• About 19 million people are blind due to cataracts.
• Glaucoma has resulted in blindness for about 6.4 million people.
• Trachoma has caused blindness in around 5.6 million victims.
• Over 1.5 million children are blind.
• An additional 10 million people have blindness due to other causes.

A significant part of the blind population, 32%, is aged between 40 and 70. Meanwhile, 60% of the blind population is over 60 years old. Every year, 2 million people go blind because of cataracts. In the general population, the blindness rate is 1.1%, and it rises to 8.5% in people over the age of 50. Alarmingly, around 7% of children have eye problems that cause poor vision.

Some eye conditions are more common in children, such as refractive error, trachoma, conjunctivitis, and malnourishment. Conditions like cataracts, conjunctivitis, and trachoma are more prevalent in women, causing a higher number of blind females. Industrial workers are more likely to go blind due to injuries from their jobs. These people are often exposed to dust, flying objects, radiation, fumes, and gases. Furthermore, blindness seems to be more prevalent among the less educated, the poor, and those with poor hygiene standards.

Signs and Symptoms of Blindness

It’s crucial to conduct a detailed patient history and physical examination when assessing a patient’s eye health. A complete history should include:

• The patient’s personal vision and eye health history
• Family history of vision and eye health
• The patient’s overall medical history, including any medications they’re taking
• Family medical history
• The patient’s social lifestyle
• The patient’s work, education, and hobbies

After getting a comprehensive history, a thorough eye examination is necessary to understand the patient’s current vision and eye function better. This exam may include:

• Testing of sight at different distances (visual acuity)
• Evaluation of the eye’s need for glasses or contact lenses (refraction)
• Checking of pupil response, eye movement, and the ability to use both eyes together
• Assessment of the entire field of vision (visual field test)
• Tests for sensitivity to glare, color perception, contrast sensitivity, and the ability to focus both eyes on a single point
• A general inspection of the eyes using a flashlight, including checking eye movements
• Close examination of the front parts of the eye (anterior segment)
• Close examination of the back parts of the eye (posterior segment)
• Testing of eye pressure (tonometry)
• Examining the angle where the iris meets the cornea (gonioscopy)

Testing for Blindness

When you go for an eye health check-up, there are several tests your doctor might carry out. These include tests to assess your visual sharpness (visual acuity), check your field of vision (visual field), evaluate the movement of your eye muscles (extraocular muscles), examine your pupils (the black part of your eyes), and test your ability to use both eyes together effectively (binocular vision testing).

The doctor will also measure the pressure inside your eyes (intraocular pressure), and closely inspect the front (anterior segment) and back (posterior segment) parts of your eyes. The back part is checked using a special test called a dilated fundus exam, which involves widening your pupils with eye drops so the doctor can get a good look at the back of your eyes.

Sometimes, other tests might be needed to help figure out what’s causing your eye problem, to keep an eye on it, or to decide on the best treatment. These could include formal field of vision tests, color vision tests, contrast sensitivity tests (which check your ability to see differences in light and dark), visual evoked potential (an electrical test to see how your brain reacts to visual stimuli), and electroretinography (another electrical test, this time to see how your retina reacts to light).

They might also use electrooculography (a test to measure the electrical activity of the layer beneath your retina), optical coherence tomography (a type of scan that gives very detailed pictures of the structures in your eye), fluorescein angiography (which uses a special dye and camera to look at blood circulation in the retina and choroid, which is the network of blood vessels that supplies the outer parts of your retina), and genetic testing (which can identify genetic eye conditions).

Treatment Options for Blindness

Comprehensive eye exams are essential in preventing, identifying, treating, and managing eye conditions that might lead to blindness. These exams should involve complete health checks for our eyes, not just checks for vision or sight-used to determine the need for glasses or contact lenses.

Many organizations worldwide are striving to raise awareness about eye health and blindness. They’re working to improve access to healthcare and combat the threat of blindness. Research is ongoing globally to understand the causes of many eye conditions leading to lasting vision loss and to develop effective treatments. The World Health Organization (WHO) leads these efforts at tracking trends, raising awareness, and coordinating actions to fight against blindness.

For patients who have low vision, rehabilitation services are available to make the most of their remaining vision, maintain their independence, and improve their quality of life. These services involve a team of professionals specialized in low vision, including optometrists, ophthalmologists, therapists, and others. More detailed information can be found in the review article titled “Low Vision Rehabilitation”.

The National Programme for Control of Blindness (NPCB) has identified various levels at which blindness can be controlled.

The first step is the Primary Assessment, done through prevalence surveys. These surveys help determine the extent, location, and causes of blindness in a given area or country.

Interventions to tackle blindness can happen at several levels. Primary Eye Care is the most grassroots level, carried out by trained workers in the community. These workers are responsible for managing basic eye conditions and referring those in need to health centers and hospitals. As part of their work, they also promote practices like proper hygiene, sanitation, and dietary management to improve eye health.

Secondary Eye Care is the next level and is focused on managing common eye conditions such as cataracts, glaucoma, and eye injuries. This care usually happens at healthcare centers and district hospitals. One key aspect of this level of eye care is mobile eye clinics, which make eye care accessible and affordable.

Tertiary Eye Care is the highest level, provided at medical colleges and institutes located in national and regional capitals. This level can deal with advanced eye procedures, offering services such as education for the blind and job creation. Additionally, specific programs are provided to tackle certain diseases and offer services like school screening, health education, and occupational eye services.

In the long run, improving one’s quality of life and preventing blindness require a focus on personal hygiene, overall nutrition, and sanitation measures.

What else can Blindness be?

Glaucoma could be caused by various factors, these include:

• Acute angle-closure glaucoma
• Primary open-angle glaucoma
• Normal tension glaucoma
• Neovascular glaucoma
• Pseudoexfoliation glaucoma
• Inflammatory glaucoma
• Traumatic glaucoma
• Glaucoma associated with intraocular tumors
• Glaucoma secondary to epithelial ingrowth
• Primary congenital glaucoma

There are also various causes of corneal conditions like:

• Fungal keratitis
• Bacterial keratitis
• Viral keratitis
• Herpes zoster ophthalmicus
• Interstitial keratitis
• Corneal dystrophies
• Graft rejection
• Bacterial hypersensitivity-mediated corneal diseases
• Mooren’s ulcer
• Keratoglobus
• Exposure keratopathy

Retinal conditions can be caused by:

• Endophthalmitis
• Diabetic retinopathy
• Nondiabetic retinopathy
• Central and branch retinal venous occlusion
• Hypertensive retinopathy
• Sickle-cell retinopathy
• Retinal detachment
• Vitreous hemorrhage

The causes for Uveal conditions can be:

• Anterior uveitis
• Posterior uveitis
• Panuveitis
• Uveitis in spondyloarthropathies
• Uveitis in juvenile idiopathic arthritis
• Vogt–Koyanagi–Harada (VKH) syndrome
• Sarcoidosis
• Parasitic uveitis
• Bacterial uveitis

Macular issues arise from conditions such as:

• Age-related macular degeneration
• Angioid streaks
• Solar retinopathy
• Chorioretinopathy
• Central serous chorioretinopathy
• Degenerative myopia

Neuro-ophthalmic disorders could be due to:

• Giant-cell arteritis
• Optic neuritis
• Papilledema
• Retrobulbar neuritis
• Arteritic ischemic optic neuropathy
• Nonarteritic ischemic optic neuropathy
• Cranial nerve palsy
• Toxic optic neuropathy
• Nutritional optic neuropathy

Lastly, Orbital disorders can be caused by:

• Thyroid eye disease
• Infections
• Noninfective inflammatory disease
• Vascular tumors
• Lymphoma
• Rhabdomyosarcoma
• Metastatic tumours
• Anophthalmic socket
• Craniosynostoses

What to expect with Blindness

The type of disease can make a person’s vision either stable or worsen over time. Some conditions, like age-related macular degeneration, only cause a loss of central vision, meaning it’s harder to see objects directly in front of you. This condition, however, will not lead to total blindness. On the other hand, retinitis pigmentosa, another eye condition, can cause loss of peripheral vision, which means you lose your side (or ‘wide’) vision. Over time, this can lead to loss of central vision and eventually complete blindness.

Eye conditions that lead to blindness can often be prevented if they are caught early. Regular eye exams can help detect these issues ahead of time. That’s why it’s important for everyone, regardless of their age, to have a comprehensive eye exam every 1 to 2 years.

For babies, there’s the InfantSEE program, which is a free public health initiative. This program provides a thorough assessment of a baby’s vision and overall eye health within their first year of life.

Possible Complications When Diagnosed with Blindness

There are many complications that can lead to loss of vision, such as:

• A break or tear in the cornea (Corneal perforation)
• An infection in the cornea (Corneal abscess)
• Cornea losing its usual structure (Corneal melt)
• Eye lens moving out of place (Lens dislocation)
• An infection in the lens (Lens abscess)
• The retina of the eye detaching from the back of the eye (Retinal detachment)
• A large tear in the retina (Giant retinal tear)
• Inflammation inside the eye (Endophthalmitis)
• Scarring of the macula at the center of the retina (Macular scar)
• Damage to the retina caused by blunt trauma (Retinal sclopetaria)
• Inflammation of the choroid and retina (Chorioretinitis)
• A tear in the thin layer of tissue lining the back of the eye (Choroidal rupture)
• Detachment of this layer from the outer part of the eye (Choroidal detachment)
• The connection between the optic nerve and the eye being pulled away (Optic disc avulsion)

Preventing Blindness

It’s crucial for someone who is legally blind to understand the importance of regular check-ups to avoid further complications. There are also steps they can take to enhance their day-to-day life. Furthermore, they should be aware that they have the right to obtain a certificate for their visual impairment. This certificate can be used to apply for government benefits to assist in managing their condition.