Continuing Education Activity

Low vision, visual impairment, and blindness are broad terms encompassing a range of conditions affecting an individual's ability to see and function in daily life. Low vision describes those whose vision cannot be fully corrected by glasses, contact lenses, refractive surgery, or other surgery. Visual impairment describes those whose decreased visual function interferes with the ability of one to perform their activities of daily living. However, the majority of causes of vision impairment can be prevented or rectified. As aging occurs, more and more blindness cases are added to the global burden, leading to an increased demand for eye healthcare services. The leading causes of blindness globally are cataracts, glaucoma, uncorrected refractive errors, age-related macular degeneration, and diabetic retinopathy. This activity provides an in-depth exploration of the various facets of blindness, low vision, and visual impairment, with a special emphasis on causes, legal interpretations, and the role of the interprofessional healthcare team in managing these patients.

Objectives:

• Identify the etiology of blindness.

• Assess vision loss based on patient evaluation.

• Implement various treatment and management options available for blindness.

• Explain interprofessional team strategies for improving coordination and outcomes in blind individuals.

Introduction

Total blindness, low vision, and visual impairment encompass a diverse range of conditions, each with its unique characteristics and implications for daily life.

Total blindness describes those who have a complete lack of light perception, documented as no light perception (NLP). Only about 15% of people with eye disorders have total blindness, and the majority of those with visual impairment have some level of vision.[1] 

Low vision describes those whose vision cannot be fully corrected by conventional methods such as glasses, contact lenses, medicine, surgery, magnification aids, or assistive technology.[2] 

Visual impairment describes those whose decreased visual function interferes with the ability of one to perform their activities of daily living, such as reading, driving, and watching TV. Visual impairment is defined based on function instead of using visual acuity or visual field cutoff values, and includes those who have low vision or who are blind.[3]

Symptoms of visual impairment include:

• Blurred vision
• Hazy/cloudiness
• Wavy or spots in central vision
• Restricted peripheral vision
• Poor night vision
• Difficulty seeing colors [4]

Legal blindness is defined by the United States Social Security Administration (SSA) to determine those who are eligible to receive disability benefits, tax exemption programs, and rehabilitation training. SSA uses visual acuity or visual field results to determine this eligibility.[5] A person is considered legally blind if he/she has central visual acuity of 20/200 or worse in the better-seeing eye with the best correction (using glasses or contact lenses) at a distance or if he/she has visual field restriction where the widest diameter is 20 degrees or less in the better-seeing eye.

There are several tests used to measure visual acuity or visual fields.[6][7] Visual acuity testing for distance is carried out using the Snellen visual acuity chart or another test that is comparable to the Snellen methodology. In 2007, SSA updated the criteria for measuring visual acuity by allowing newer low-vision test charts to be used instead of Snellen acuity charts alone. Under this update, if a person cannot read at least one letter on the 20/100 line, he or she will be classified as legally blind.[8] 

Acceptable tests for visual field testing include automated static perimetry such as Humphrey Field Analyzer (HFA) 30-2, HFA 24-2, and Octopus 32, kinetic perimetry such as Goldmann perimetry or HFA "SSA Test Kinetic." Screening tests, including confrontation tests, tangent screen tests, and static screening tests, are not accepted forms of testing to determine legal blindness.

The World Health Organization (WHO) classifies visual impairment into the following categories based on visual acuity or a visual field of the better-seeing eye. 

• Normal: 20/10-20/25
• Near normal visual impairment: 20/30-20/60
• Moderate visual impairment: 20/70-20/160
• Severe visual impairment: 20/200-20/400 or 11-20 degrees on visual field
• Profound visual impairment: 20/500-20/1000 visual acuity or 6- 10 degrees on visual field
• Near total visual impairment: Counting fingers, hand motion, light perception, or 5 degrees or less on visual field
• Total visual impairment: No light perception 

WHO also defines blindness as visual acuity of 3/60 (Snellen’s chart) or less or its equivalent (see Table. WHO and the National Programme on Control of Blindness [NPCB] classification of blindness). In the absence of visual acuity charts, when paramedical staff takes the visual acuity, it is defined as the inability to count fingers at a distance of 3 meters in daylight to indicate 3/60 or its equivalent.[9]

Table. WHO and the National Programme on Control of Blindness (NPCB) classification of blindness [1]

Etiology

There can be many different causes of blindness. The leading causes of blindness worldwide are cataracts, age-related macular degeneration, glaucoma, diabetic retinopathy, and trachoma.[10]

• Cataracts: A condition that causes yellowing and hardening of the lens in the eye; the leading cause of blindness worldwide in developing and developed countries
• Age-related macular degeneration: A condition that damages a part of the retina known as the macula; the leading cause of blindness in Caucasians and those aged 65 and older
• Glaucoma: A condition that damages the optic nerve; the leading cause of blindness in African Americans
• Diabetic retinopathy: A condition due to systemic diabetes; the leading cause of new blindness in adults between 25 and 64 
• Trachoma: A condition caused by the Chlamydia trachomatis bacteria; incidence is decreasing due to public health action [11]

The number of persons with reduced vision due to uncorrected refractive error exceeds that of those with the conditions mentioned above. However, uncorrected refractive errors can be easily treated or "cured" with proper vision correction.

Estimates are that approximately 90% of the visually impaired population lives in developing countries or low-income circumstances. About 80% of all visual impairments worldwide can be prevented, treated, or cured with proper eye care.

The most common causes of blindness are:

• Cataracts (51%)
• Glaucoma (8%)
• Age-related macular degeneration (5%)
• Corneal opacification (4%)
• Childhood blindness (4%)
• Refractive errors (3%)
• Trachoma (3%)
• Diabetic retinopathy (1%)
• Undetermined (21%)

In developed countries, the major causes of blindness are:

• Trauma
• Glaucoma
• Diabetic retinopathy
• Vascular occlusions
• Cataract
• Age-related macular degeneration

 In children, the major causes of blindness are:

• Xerophthalmia
• Congenital glaucoma
• Congenital cataract
• Optic atrophy
• Trauma
• Amblyopia
• Refractive errors
• Trachoma [12]

Epidemiology

According to WHO, approximately 285 million people have a visual impairment, including 39 million who are blind and 246 million who have low vision. Of those who are blind, 90% live in developing countries. For each blind person worldwide, an average of 3.4 people have low vision, with the country and regional variation ranging from 2.4 to 5.5 people.[10][13] According to another report, 180 million people worldwide are visually disabled, including 45 million who are blind (80% of this blindness is preventable).[14]

More than 82% of all people who are blind are 50 years of age and older. Due to the expected number of years lived in blindness, childhood blindness is a significant problem, with an estimated 1.4 million children under age 15 who are blind. Females have a significantly higher risk of being visually impaired than males.[15]

Approximate prevalence of blindness due to various causes:

• Cataracts: 19 million
• Glaucoma: 6.4 million
• Trachoma: 5.6 million
• Childhood blindness: >1.5 million
• Other causes: 10 million [16]

A sizeable portion of the blind population (32%) is between 40 and 70 years old, and 60% is over 60 years old. The yearly incidence of blindness due to cataracts is 2 million cases. According to the national survey analysis on blindness 2001-2002, the estimated prevalence of blindness is 8.5% in the over-50 age group and 1.1% in the general population. Approximately 7% of children are suffering from ocular conditions leading to low vision and problems with eyesight.[17]

Some of the ocular conditions leading to blindness are more common in children, such as refractive error, trachoma, conjunctivitis, and malnourishment.[18] The ocular conditions more common in women are cataracts, conjunctivitis, and trachoma, leading to a greater prevalence of blindness in women. Occupation-related blindness is more common in factory workers, workshops, and industrial workers who are more prone to penetrating and perforating injuries. These people are more exposed to dust, flying objects and particles, radiation, fumes, and gases.[19] As per previous studies, it has been documented that blindness is more common in poor socioeconomic strata, people with low education, poor patients, and patients with low standards of personal and community hygiene.[20]

Pathophysiology

Conditions causing visual impairment vary widely and can be genetic, congenital, or acquired. Vision loss can occur gradually or suddenly and can result in central vision loss, peripheral vision loss, overall blur, a decrease in contrast sensitivity, color vision difficulties, night vision blindness, and glare or light sensitivity issues. The cause of vision loss determines whether it involves one type alone or a combination of presentations.[21][22]

History and Physical

Performing a thorough case history is essential. The case history should include:

• Patient's visual and ocular history
• Family visual and ocular history
• Patient medical history, including medications
• Family medical history
• Social history
• Vocational, educational, and hobby history [23]

Subsequently, an ocular examination is necessary to assess the patient's current visual status and function; it should include: 

• Visual acuity (distance and near)
• Refraction
• Pupils, motility, and binocular vision
• Visual fields (central and peripheral fields of vision)
• Glare testing, color vision, contrast sensitivity, binocular single vision
• Gross examination on torch light, including ocular movements
• Detailed anterior segment examination
• Detailed posterior segment examination
• Tonometry (intraocular pressure measurement)
• Gonioscopy [24]

Evaluation

An ocular health examination should typically include visual acuity, visual field, extraocular muscles, pupil, binocular vision testing, intraocular pressure, anterior segment, and posterior segment evaluation with dilated fundus exams. Supplemental testing such as formalized visual field testing, color vision tests, contrast sensitivity tests, visual evoked potential, electroretinography, electrooculography, optical coherence tomography, fluorescein angiography, and genetic testing may be necessary to help determine the etiology and to monitor and properly manage the condition.[25]

Treatment / Management

Comprehensive eye examinations are necessary to prevent, detect, treat, and manage the ocular conditions that can lead to blindness. Eye exams should include ocular health exams and not just vision and sight checks for glasses or contact lens prescriptions.[26]

Many international, national, and local organizations are working to bring more awareness about vision and eye health, provide access to healthcare, and fight blindness. Research is being done worldwide to study the etiologies of many eye conditions causing permanent vision loss and to develop a proper treatment to control or cure these conditions. WHO is the leader in monitoring trends, raising awareness, and coordinating efforts to fight blindness.[27]

Low-vision rehabilitation services are available to help patients maximize their remaining vision, maintain their independence, and improve their quality of life.[28] These services are provided by a multidisciplinary team of low-vision professionals, including low-vision doctors (optometrists or ophthalmologists), low-vision therapists, occupational therapists, rehabilitation teachers, orientation and mobility specialists, vocational rehabilitation specialists, social workers, and other rehabilitation low-vision professionals. Please refer to the review article titled "Low Vision Rehabilitation" for additional information.[29]

As determined by NPCB, there are various levels at which blindness is controlled.

Primary Assessment

Primary Assessment is performed by prevalence surveys. It is necessary to assess the magnitude, geographical distribution of pathology, and etiology of blindness within a particular town, place, or country.[30]

Intervention

Primary Eye Care

Primary eye care is the management of eye conditions at the grassroots level by trained workers. The paramedical staff is the first to make contact with people in the community. The staff is trained and dedicated to referring needy patients to the nearest primary health center and district hospitals. They also help promote practices such as basic hygiene, sanitation, dietary management, and the safety of patients. The main aim is to improve the quality of eyecare by primary eye care approach and improve the quality of present resources.[31]

Secondary Eye Care

This involves the management of common ocular conditions such as cataracts, trichiasis, glaucoma, ocular trauma, and entropion. Secondary eye care is taken care of at primary healthcare centers and district hospitals where there are well-developed eye departments. A strong component of secondary eye care is mobile eye clinics. This strategy's main advantage is treating problem-specific concerns, utilizing local resources, and providing cost-effective eye care to the population at a peripheral level.[32]

Tertiary Eye Care

This level of eyecare is provided at the national and regional capitals and is provided at the level of medical colleges and medical institutes. The ocular pathologies that can be managed at this level are retinal surgeries in retinal detachment, corneal transplant, trabeculectomy, orbitotomy, etc, which are not available at secondary centers. The other services offered are the education of blind people and service utilization for creating employment. The various special programs offered for disease-specific control are trachoma control, xerophthalmia measures with vitamin A prophylaxis, school screening, health education, and occupational eye services.[33]

Long-term Outcomes

To improve quality of life, hygiene, nutrition, personal hygiene, and sanitation measures must be taken into consideration.[34]

Differential Diagnosis

Glaucoma Causes

• Acute angle-closure glaucoma
• Primary open-angle glaucoma [35]
• Primary angle-closure glaucoma
• Normal tension glaucoma
• Neovascular glaucoma
• Malignant glaucoma
• Pseudoexfoliation glaucoma
• Inflammatory glaucoma
• Lens-induced glaucoma
• Traumatic glaucoma
• Iridocorneal endothelial syndrome
• Glaucoma associated with intraocular tumors
• Glaucoma secondary to epithelial ingrowth
• Primary congenital glaucoma
• Iridocorneal dysgenesis
• Glaucoma in phacomatoses

Corneal Causes

• Fungal keratitis
• Bacterial keratitis
• Viral keratitis
• Pythium keratitis [36][37][38][39]
• Herpes zoster ophthalmicus
• Interstitial keratitis
• Protozoan keratitis
• Corneal dystrophies
• Graft rejection
• Helminthic keratitis
• Bacterial hypersensitivity-mediated corneal diseases
• Rosacea keratitis
• Peripheral ulcerative keratitis
• Mooren’s ulcer
• Penetrating and perforating corneal injuries
• Keratoconus
• Keratoglobus
• Pellucid marginal degeneration
• Exposure keratopathy
• Congenital anomalies of the cornea
• Neurotrophic keratitis
• Chemical injury
• Thermal injury

Retinal Causes

• Endophthalmitis
• Diabetic retinopathy
• Nondiabetic retinopathy
• Central and branch retinal venous occlusion
• Central retinal arterial occlusion
• Ocular ischaemic syndrome
• Hypertensive retinopathy
• Sickle-cell retinopathy
• Thalassaemia retinopathy
• Retinopathy of prematurity
• Retinal artery macroaneurysm
• Primary retinal telangiectasia
• Eales disease
• Radiation retinopathy
• Purtscher retinopathy
• Valsalva retinopathy
• Lipaemia retinalis
• Retinopathy in blood disorders
• Retinal detachment
• Intraretinal foreign body
• Vitreous hemorrhage

Uveal Causes

• Anterior uveitis
• Intermediate uveitis
• Posterior uveitis
• Panuveitis
• Uveitis in spondyloarthropathies
• Fuchs uveitis syndrome
• Uveitis in juvenile idiopathic arthritis
• Uveitis in bowel disease
• Uveitis in renal disease
• Intermediate uveitis
• Vogt–Koyanagi–Harada (VKH) syndrome
• Sympathetic ophthalmitis
• Lens-induced uveitis
• Sarcoidosis
• Behçet disease
• Parasitic uveitis
• Viral uveitis
• Fungal uveitis
• Bacterial uveitis
• Sclerokeratouveitis

 Macular Causes

• Age-related macular degeneration
• Angioid streaks
• Choroidal folds
• Hypotony maculopathy
• Solar retinopathy
• Focal choroidal excavation
• Retinal angiomatous proliferation
• Polypoidal choroidal vasculopathy
• Peripheral exudative haemorrhagic
• Chorioretinopathy
• Idiopathic choroidal neovascularization
• Vitreomacular interface disorders
• Central serous chorioretinopathy
• Idiopathic macular telangiectasia
• Cystoid macular edema
• Microcystic macular edema
• Degenerative myopia

 Neuro-ophthalmic Causes

• Giant-cell arteritis
• Optic neuritis
• Papilledema
• Retrobulbar neuritis
• Orbital apex syndrome
• Arteritic ischemic optic neuropathy
• Nonarteritic ischemic optic neuropathy
• Cranial nerve palsy
• Tolosa-Hunt syndrome
• Foster Kennedy syndrome
• Pseudo–Tolosa-Hunt syndrome
• Toxic optic neuropathy
• Nutritional optic neuropathy

Orbital Causes

• Thyroid eye disease
• Infections
• Noninfective inflammatory disease
• Nonneoplastic vascular abnormalities
• Cystic lesions
• Vascular tumors
• Lacrimal gland tumors
• Neural tumours
• Lymphoma
• Rhabdomyosarcoma
• Metastatic tumours
• Anophthalmic socket
• Craniosynostoses

Prognosis

Depending on the condition, vision can be stable or progressive in nature. Conditions such as age-related macular degeneration only cause central vision loss and will not result in total blindness, whereas retinitis pigmentosa can cause peripheral vision loss leading to central vision loss and total blindness. Conditions causing blindness may be prevented with early detection, proper diagnosis, and treatment. It is recommended that people of all ages have a comprehensive eye examination every 1 to 2 years. For infants, InfantSEE is a free public health program available to provide comprehensive infant vision and eye health assessment within the first year of the infant's life.[40] 

Complications

Complications that can cause blindness include:

• Corneal perforation
• Corneal abscess
• Corneal melt
• Lens dislocation
• Lens abscess
• Retinal detachment
• Giant retinal tear
• Endophthalmitis
• Macular scar
• Retinal sclopetaria
• Chorioretinitis
• Choroidal rupture
• Choroidal detachment
• Optic disc avulsion

Consultations

Any patient with sudden onset loss of vision should be evaluated by an ophthalmologist to rule out the cause of blindness. A meticulous ophthalmic examination is warranted in each to pinpoint the ocular pathology. Appropriate specialist consultation should be sought after screening if needed.[41]

Deterrence and Patient Education

A patient who is legally blind should be educated on the need for regular follow-up to prevent the development of further complications, as well as what measures can be taken to improve their lifestyle. A person with ocular disability and blindness should be advised that he or she is entitled to receive the ocular disability certificate and can apply for government benefits.[42]

Pearls and Other Issues

Blindness has affected millions worldwide, and it is the duty of ophthalmologists and paramedical staff to reduce this burden. A person with an ocular disability, if managed on time, can be prevented from developing irregular ocular sequelae. The cause of blindness should be ruled out in each case.[16]

Enhancing Healthcare Team Outcomes

Blindness in all its forms and severities confers serious morbidity to those affected, whether total blindness or visual impairments that include transient blindness or partial loss of field of vision. The assessment, diagnosis, and management of vision loss requires an interprofessional team approach, including physicians, specialists, specialty-trained nurses, optometrists, and pharmacists, all collaborating across disciplines to achieve optimal patient results.[43]