Childhood blindness

Last updated
Childhood blindness
Snellen chart.svg
Snellen chart used to determine visual acuity
CausesGenetic disorder, Infection [1]
Diagnostic method Pupillary reflex(among others) [2]
PreventionVitamin A supplement

Childhood blindness is an important contribution to the national prevalence of the disability of blindness. [3] Blindness in children can be defined as a visual acuity of <3/60 in the eye with better vision of a child under 16 years of age. [4] This generally means that the child cannot see an object 10 feet (about 3 meters) away, that another child could see if it was 200 feet (about 60 meters) away. [5]

Contents

Causes

There are many causes of blindness in children. Blindness may be due to genetic mutations, birth defects, premature birth, nutritional deficiencies, infections, injuries, and other causes. Severe retinopathy of prematurity (ROP), cataracts, Vitamin A deficiency, measles, conjunctivitis and refractive error are also causes. [6] [7]

Vitamin A deficiency

Vitamin A deficiency is most common in developing countries where many kids experience malnourishment. This vitamin deficiency blinds hundreds of thousands of kids each year, and is a preventable cause of childhood blindness. Since vitamin A is required for rhodopsin, the photosensitive pigment in the retinol rods, its deficiency can lead to night blindness. [8]

Measles

Since 2010, globally 85% of children have been vaccinated for measles significantly reducing the number of measles cases each year. Children who have a vitamin A deficiency and measles infection can develop corneal ulcerations and keratomalacia due to immunosuppression caused by the vitamin deficiency. [8]

Newborn conjunctivitis

Newborn conjunctivitis is present at the time of birth and presents within the first 28 days of life as a severe conjunctival infection with purulent discharge. This increases the risk of corneal ulcerations and perforations that can lead to blindness. The common organisms that lead to this diagnosis include Neisseria gonorrhoea and Chlamydia trachomatis. Infected pregnant women and their partners should be treated to avoid infection of the newborn, and newborns presenting with conjunctivitis should be treated with hourly topical antibiotic drops (gentamicin). [8]

Retinopathy of prematurity

Retinopathy of Prematurity (ROP) is classified by the abnormal growth of blood vessels in the retina, a process called retinal neovascularization. [9] These blood vessels may bleed or grow in the wrong direction. Bleeding can lead to the formation of scar tissue which can cause blurred vision and vision loss. If the vessels grow too far in the wrong direction, they can pull the retina away from the back of the eye – this is called retinal detachment. Retinal detachment is a medical emergency that can cause permanent blindness and thus requires urgent intervention. [10]

Babies who are born prematurely (formally defined as 37 weeks of gestational age or earlier) are at higher risk of developing retinopathy of prematurity. The earlier a preterm baby is born, the greater the baby's risk of developing ROP. Blood vessels in the eye typically finish development by the time of birth. Therefore, a baby who is born early is exposed to various stimuli (oxygen, lights, temperature, etc.) that may influence how the blood vessels of the eye develop. Additional risk factors for ROP include low birth weight (3 pounds or less) and giving the baby extra oxygen following birth. If preterm infants are experiencing other health problems like anemia, vitamin E deficiency, and/or breathing problems, they are at increased risk of developing ROP. [11]

Mechanism

Human Eye Three Main Layers of the Eye.png
Human Eye

Childhood blindness has many causes. [12] Leading causes include retinopathy of prematurity, vitamin A deficiency, infectious diseases (measles, newborn conjunctivitis), retinoblastoma, and congenital conditions (cataracts and glaucoma). [13] Leber congenital amaurosis primarily affects the retina, and typically severe visual impairment begins in infancy. Mutations in Aryl hydrocarbon receptor interacting protein like-1 have been linked to Leber congenital amaurosis (LCA). [14]

The most frequently affected parts of the eyes are: [15] [16]

Diagnosis

The diagnosis of childhood blindness is done via methods to ascertain the degree of visual impairment in the affected child. Early detection is essential to provide early intervention to children. The American Academy of Ophthalmology recommend various screening methods starting in newborns and spanning throughout childhood in order to assess for childhood blindness and other ophthalmic disorders. Newborns are screened with the red reflex test performed by shining a light into the child's eyes. If a red reflex is not produced, further workups should be done to assess for congenital cataracts or retinoblastoma. From 6-12 months, children are screened at their well-child visits with the red reflex test, assessment of eye movement, and proper pupil dilation. From 1 year to 3 years of age, children often undergo a "photoscreening" test where a camera takes pictures of the child's eyes to assess for developmental abnormalities that may lead to amblyopia. Children ages 3 to 5 years of age will be assessed for proper eye alignment and visual acuity. Visual acuity is assessed with a Snellen chart with lines of letters that the child reads and helps determine visual acuity. [17]

Prevention

The chemical structure of Vitamin A (one of many chemical forms) All-trans-Retinol.svg
The chemical structure of Vitamin A (one of many chemical forms)

Vitamin A Deficiency

Vitamin A deficiency is a leading cause of preventable childhood blindness, particularly in developing countries. Vitamin A deficiency is defined as a serum (blood) concentration of less than 0.70 µmol/L while a severe deficiency is defined as less than 0.35 µmol/L, per the Centers of Disease Control National Health and Nutrition Examination Survey. [18] Vitamin A is supplied through the diet, and a deficiency often results from poor dietary intake of Vitamin A-rich foods. [19] Low dietary levels of Vitamin A can be worsened by infections that cause inflammation in the gastrointestinal tract, which prevent the body from fully absorbing Vitamin A available within digested food. Children in the United States have a recommended Vitamin A dietary allowance of at least 300 micrograms/day. [19] Good sources of Vitamin A include vegetables, such as carrots, papaya, and pumpkin. [20] Animal products, such as fish oils, as well as dairy products (milk, cheese, and yogurt) are also sources of Vitamin A. [20]

Retinopathy of Prematurity

Retinopathy of prematurity (ROP) is a cause of childhood blindness that can occur around the time of birth. Generally, measures taken to avoid preterm birth are also effective at preventing ROP. Babies delivered preterm, defined at or before 37 weeks of gestation, have incomplete development of the blood vessels supplying the retina. [21] At birth, increased exposure to oxygen from the environment and from medical interventions (such as a high flow nasal cannula) causes damage to retinal blood vessels and stunts their growth. Prevention of ROP in preterm babies involves careful monitoring of oxygen delivery to avoid excess exposure. [22] Neonatal ocular exams can help detect ROP. [23]

Treatment

Whether blindness is treatable depends upon the cause. [24] Surgical intervention can be performed in cases of primary congenital glaucoma. A 2020 review found no difference between combined trabeculotomy and trabeculectomy (CTT) and routine conventional trabeculotomy, or between visco-trabeculotomy and routine conventional trabeculotomy. The review also found that the 360-degree circumferential trabeculotomy may show greater surgical success than conventional trabeculotomy but that further research with one year follow-up was needed. [25]

Braille Braille closeup.jpg
Braille

Management

Braille is a universal way to learn how to read and write, for the blind. [26] A refreshable braille display is an assistive learning device that can help such children in school. [27] Schools for the blind are a form of management, however the limitations of using studies done in such schools has been recognized. Children that are enrolled presently usually developed blindness 5 or more years prior to enrollment, consequently not reflecting current possible causes. [28] About 66% of children with visual impairment also have one other disability (comorbidity), be it, intellectual disabilities, cerebral palsy, or hearing loss. [29] Eye care/screening for children within primary health care is important, as catching ocular disease issues can lead to better outcomes overall. [30]

Epidemiology

Globally, the number children with blindness is approximately 1.4 million, representing 4% of the global blind population, and an additional 17.5 million are at risk of developing poor vision. [31] Although this number is significantly lower than the number of blind adults, the estimated economic and social burden of blindness for children is much greater due to the increase in blind years. Childhood blindness is most prevalent among children with genetic ancestry from Africa and Asia, who represent 75% of the world's affected population. [13] [32] A 2014 review indicated that an estimated 238,500 children with bilateral blindness (rate 1.2/1,000) live in the Eastern Mediterranean region. [30] There is also an increase in blindness outside of developing countries due to a lack of screening and prophylactic measures to treat causes of pediatric blindness. [33]

Society and culture

VISION 2020 is a program launched by the International Agency for the Prevention of Blindness (IAPB) and is supported by the WHO in 1999 that has made controlling blindness in children a high priority. [34] In addition, the IAPB and WHO coordinate "World Sight Day" on the second Thursday of October each year. [35] Starting in 2000, World Sight Day has become an opportunity to raise awareness of eye health and highlight the importance of increasing access to eye health services globally. It has also become a tool to influence governments around the world to allocate funds for blindness prevention programs and educational initiatives.

Related Research Articles

<span class="mw-page-title-main">Retina</span> Part of the eye

The retina is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then processes that image within the retina and sends nerve impulses along the optic nerve to the visual cortex to create visual perception. The retina serves a function which is in many ways analogous to that of the film or image sensor in a camera.

<span class="mw-page-title-main">Retinopathy</span> Medical condition

Retinopathy is any damage to the retina of the eyes, which may cause vision impairment. Retinopathy often refers to retinal vascular disease, or damage to the retina caused by abnormal blood flow. Age-related macular degeneration is technically included under the umbrella term retinopathy but is often discussed as a separate entity. Retinopathy, or retinal vascular disease, can be broadly categorized into proliferative and non-proliferative types. Frequently, retinopathy is an ocular manifestation of systemic disease as seen in diabetes or hypertension. Diabetes is the most common cause of retinopathy in the U.S. as of 2008. Diabetic retinopathy is the leading cause of blindness in working-aged people. It accounts for about 5% of blindness worldwide and is designated a priority eye disease by the World Health Organization.

<span class="mw-page-title-main">Retinitis pigmentosa</span> Gradual retinal degeneration leading to progressive sight loss

Retinitis pigmentosa (RP) is a genetic disorder of the eyes that causes loss of vision. Symptoms include trouble seeing at night and decreasing peripheral vision. As peripheral vision worsens, people may experience "tunnel vision". Complete blindness is uncommon. Onset of symptoms is generally gradual and often begins in childhood.

The National Eye Institute (NEI) is part of the U.S. National Institutes of Health (NIH), an agency of the U.S. Department of Health and Human Services. The mission of NEI is “to eliminate vision loss and improve quality of life through vision research.” NEI consists of two major branches for research: an extramural branch that funds studies outside NIH and an intramural branch that funds research on the NIH campus in Bethesda, Maryland. Most of the NEI budget funds extramural research.

Retinopathy of prematurity (ROP), also called retrolental fibroplasia (RLF) and Terry syndrome, is a disease of the eye affecting prematurely born babies generally having received neonatal intensive care, in which oxygen therapy is used due to the premature development of their lungs. It is thought to be caused by disorganized growth of retinal blood vessels which may result in scarring and retinal detachment. ROP can be mild and may resolve spontaneously, but it may lead to blindness in serious cases. Thus, all preterm babies are at risk for ROP, and very low birth-weight is an additional risk factor. Both oxygen toxicity and relative hypoxia can contribute to the development of ROP.

This is a partial list of human eye diseases and disorders.

<span class="mw-page-title-main">Nyctalopia</span> Condition making it difficult or impossible to see in relatively low light

Nyctalopia, also called night-blindness, is a condition making it difficult or impossible to see in relatively low light. It is a symptom of several eye diseases. Night blindness may exist from birth, or be caused by injury or malnutrition. It can be described as insufficient adaptation to darkness.

<span class="mw-page-title-main">Xerophthalmia</span> Dry eye

Xerophthalmia is a medical condition in which the eye fails to produce tears. It may be caused by vitamin A deficiency, which is sometimes used to describe that condition, although there may be other causes.

Retinal hemorrhage is a disorder of the eye in which bleeding occurs in the retina, the light sensitive tissue, located on the back wall of the eye. There are photoreceptor cells in the retina called rods and cones, which transduce light energy into nerve signals that can be processed by the brain to form visual images. Retinal hemorrhage is strongly associated with child abuse in infants and young children and often leaves such abused infants permanently blind. In older children and adults, retinal hemorrhage can be caused by several medical conditions such as hypertension, retinal vein occlusion, anemia, leukemia or diabetes.

<span class="mw-page-title-main">Electroretinography</span>

Electroretinography measures the electrical responses of various cell types in the retina, including the photoreceptors, inner retinal cells, and the ganglion cells. Electrodes are placed on the surface of the cornea or on the skin beneath the eye to measure retinal responses. Retinal pigment epithelium (RPE) responses are measured with an EOG test with skin-contact electrodes placed near the canthi. During a recording, the patient's eyes are exposed to standardized stimuli and the resulting signal is displayed showing the time course of the signal's amplitude (voltage). Signals are very small, and typically are measured in microvolts or nanovolts. The ERG is composed of electrical potentials contributed by different cell types within the retina, and the stimulus conditions can elicit stronger response from certain components.

Visual impairment, also known as vision impairment, is a medical definition primarily measured based on an individual's better eye visual acuity; in the absence of treatment such as corrective eyewear, assistive devices, and medical treatment– visual impairment may cause the individual difficulties with normal daily tasks including reading and walking. Low vision is a functional definition of visual impairment that is chronic, uncorrectable with treatment or conventional corrective lenses, and impacts daily living. As such low vision can be used as a disability metric and varies based on an individual's experience, environmental demands, accommodations, and access to services. The American Academy of Ophthalmology defines visual impairment as the best-corrected visual acuity of less than 20/40 in the better eye, and the World Health Organization defines it as a presenting acuity of less than 6/12 in the better eye. The term blindness is used for complete or nearly complete vision loss. In addition to the various permanent conditions, fleeting temporary vision impairment, amaurosis fugax, may occur, and may indicate serious medical problems. The abbreviation VIP is sometimes used for Visually Impaired Person, Persons or People.

Neovascularization is the natural formation of new blood vessels, usually in the form of functional microvascular networks, capable of perfusion by red blood cells, that form to serve as collateral circulation in response to local poor perfusion or ischemia.

Eales disease is a type of obliterative vasculopathy, also known as angiopathia retinae juvenilis, periphlebitis retinae or primary perivasculitis of the retina. It was first described by the British ophthalmologist Henry Eales (1852–1913) in 1880 and is a rare ocular disease characterized by inflammation and possible blockage of retinal blood vessels, abnormal growth of new blood vessels (neovascularization), and recurrent retinal and vitreal hemorrhages.

The red reflex refers to the reddish-orange reflection of light from the back of the eye, or fundus, observed when using an ophthalmoscope or retinoscope. The reflex relies on the transparency of optical media and reflects off the fundus back through media into the aperture of the ophthalmoscope. The red reflex is considered abnormal if there is any asymmetry between the eyes, dark spots, or white reflex (Leukocoria).

<span class="mw-page-title-main">Blurred vision</span> Medical condition

Blurred vision is an ocular symptom where vision becomes less precise and there is added difficulty to resolve fine details.

<span class="mw-page-title-main">Intraocular hemorrhage</span> Medical condition

Intraocular hemorrhage is bleeding inside the eye. Bleeding can occur from any structure of the eye where there is vasculature or blood flow, including the anterior chamber, vitreous cavity, retina, choroid, suprachoroidal space, or optic disc.

Autoimmune retinopathy (AIR) is a rare disease in which the patient's immune system attacks proteins in the retina, leading to loss of eyesight. The disease is poorly understood, but may be the result of cancer or cancer chemotherapy. The disease is an autoimmune condition characterized by vision loss, blind spots, and visual field abnormalities. It can be divided into cancer-associated retinopathy (CAR) and melanoma-associated retinopathy (MAR). The condition is associated with retinal degeneration caused by autoimmune antibodies recognizing retinal proteins as antigens and targeting them. AIR's prevalence is extremely rare, with CAR being more common than MAR. It is more commonly diagnosed in females in the age range of 50–60.

<span class="mw-page-title-main">Congenital blindness</span>

Congenital blindness refers to blindness present at birth. Congenital blindness is sometimes used interchangeably with "Childhood Blindness." However, current literature has various definitions of both terms. Childhood blindness encompasses multiple diseases and conditions present in ages up to 16 years old, which can result in permanent blindness or severe visual impairment over time. Congenital blindness is a hereditary disease and can be treated by gene therapy. Visual loss in children or infants can occur either at the prenatal stage or postnatal stage. There are multiple possible causes of congenital blindness. In general, 60% of congenital blindness cases are contributed from prenatal stage and 40% are contributed from inherited disease. However, most of the congenital blindness cases show that it can be avoidable or preventable with early treatment.

Sickle cell retinopathy can be defined as retinal changes due to blood vessel damage in the eye of a person with a background of sickle cell disease. It can likely progress to loss of vision in late stages due to vitreous hemorrhage or retinal detachment. Sickle cell disease is a structural red blood cell disorder leading to consequences in multiple systems. It is characterized by chronic red blood cell destruction, vascular injury, and tissue ischemia causing damage to the brain, eyes, heart, lungs, kidneys, spleen, and musculoskeletal system.

Drug abuse retinopathy is damage to the retina of the eyes caused by chronic drug abuse. Types of retinopathy caused by drug abuse include maculopathy, Saturday night retinopathy, and talc retinopathy. Common symptoms include temporary and permanent vision loss, blurred vision, and night blindness. Substances commonly associated with this condition include poppers, heroin, cocaine, methamphetamine, tobacco, and alcohol.

References

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  2. ↑ Gogate, Parikshit; Gilbert, Clare; Zin, Andrea (2011). "Severe Visual Impairment and Blindness in Infants: Causes and Opportunities for Control". Middle East African Journal of Ophthalmology. 18 (2): 109–114. doi: 10.4103/0974-9233.80698 . ISSN   0974-9233. PMC   3119278 . PMID   21731320.
  3. ↑ GLOBAL DATA ON VISUAL IMPAIRMENTS 2010 (PDF). WHO. 2012. p. 6.
  4. ↑ Mabey, David; Gill, Geoffrey; Weber, Martin W.; Whitty, Christopher J. M. (2013-01-17). Principles of Medicine in Africa. Cambridge University Press. ISBN   9781107002517.
  5. ↑ "The criteria for certification". RNIB - See differently. 19 February 2014.
  6. ↑ Gilbert, Clare; Muhit, Mohammed (2008). "Twenty years of childhood blindness: what have we learnt?". Community Eye Health. 21 (67): 46–47. ISSN   0953-6833. PMC   2580065 . PMID   19030129.
  7. ↑ International Committee for the Classification of Retinopathy of Prematurity (July 1, 2005). "THe international classification of retinopathy of prematurity revisited". Archives of Ophthalmology. 123 (7): 991–999. doi: 10.1001/archopht.123.7.991 . ISSN   0003-9950. PMID   16009843.
  8. 1 2 3 Beare, Nicholas A.V.; Bastawrous, Andrew (2014), "Ophthalmology in the Tropics and Sub-tropics", Manson's Tropical Infectious Diseases, Elsevier, pp. 952–994.e1, doi:10.1016/b978-0-7020-5101-2.00068-6, ISBN   9780702051012 , retrieved 2022-09-12
  9. ↑ "Retinopathy of Prematurity | National Eye Institute". www.nei.nih.gov. Retrieved 2022-09-13.
  10. ↑ "Retinal detachment - Symptoms and causes". Mayo Clinic. Retrieved 2022-09-14.
  11. ↑ "What Is Retinopathy of Prematurity (ROP)?". American Academy of Ophthalmology. 2022-05-11. Retrieved 2022-09-14.
  12. ↑ Hartnett, Mary Elizabeth (2005-01-01). Pediatric Retina. Lippincott Williams & Wilkins. ISBN   9780781747820.
  13. 1 2 Beare, Nicholas A. V.; Bastawrous, Andrew (2014-01-01), Farrar, Jeremy; Hotez, Peter J.; Junghanss, Thomas; Kang, Gagandeep (eds.), "67 - Ophthalmology in the Tropics and Sub-tropics", Manson's Tropical Infectious Diseases (Twenty-third Edition), London: W.B. Saunders, pp. 952–994.e1, ISBN   978-0-7020-5101-2 , retrieved 2022-09-12
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  15. ↑ Bhattacharjee, H; Das, K; Borah, RR; Guha, K; Gogate, P; Purukayastha, S; Gilbert, C (Nov–Dec 2008). "Causes of childhood blindness in the northeastern states of India". Indian Journal of Ophthalmology. 56 (6): 495–9. doi: 10.4103/0301-4738.43368 . PMC   2612985 . PMID   18974521.
  16. ↑ Ezegwui, IR; Umeh, RE; Ezepue, UF (Jan 2003). "Causes of childhood blindness: results from schools for the blind in south eastern Nigeria". The British Journal of Ophthalmology. 87 (1): 20–3. doi:10.1136/bjo.87.1.20. PMC   1771452 . PMID   12488255.
  17. ↑ "Eye Screening for Children". American Academy of Ophthalmology. 2021-03-23. Retrieved 2022-08-29.
  18. ↑ Pfeiffer, Christine M.; Sternberg, Maya R.; Schleicher, Rosemary L.; Haynes, Bridgette M.H.; Rybak, Michael E.; Pirkle, James L. (April 2013). "CDC's Second National Report on Biochemical Indicators of Diet and Nutrition in the US Population is a valuable tool for researchers and policy makers". The Journal of Nutrition. 143 (6): 938S–947S. doi:10.3945/jn.112.172858. ISSN   0022-3166. PMC   4822995 . PMID   23596164.
  19. 1 2 Hodge, Christopher; Taylor, Christopher (2022), "Vitamin A Deficiency", StatPearls, Treasure Island (FL): StatPearls Publishing, PMID   33620821 , retrieved 2022-09-12
  20. 1 2 Hombali, Aditi S; Solon, Juan Antonio; Venkatesh, Bhumika T; Nair, N Sreekumaran; Peña‐Rosas, Juan Pablo (2019-05-10). "Fortification of staple foods with vitamin A for vitamin A deficiency". The Cochrane Database of Systematic Reviews. 2019 (5): CD010068. doi:10.1002/14651858.CD010068.pub2. ISSN   1469-493X. PMC   6509778 . PMID   31074495.
  21. ↑ Smith, Lois E. H. (2004-06-01). "Pathogenesis of retinopathy of prematurity". Growth Hormone & IGF Research. Proceedings of the 35th International Symposium on Growth Hormone and Growth Factors in Endocrinology and Metabolism. 14: 140–144. doi:10.1016/j.ghir.2004.03.030. ISSN   1096-6374. PMID   15135797.
  22. ↑ Liegl, Raffael; Hellström, Ann; Smith, Lois EH (2016-05-20). "Retinopathy of prematurity: the need for prevention". Eye and Brain. 8: 91–102. doi: 10.2147/EB.S99038 . ISSN   1179-2744. PMC   5398747 . PMID   28539804.
  23. ↑ "Retinopathy of Prematurity | National Eye Institute". www.nei.nih.gov. Retrieved 2022-09-12.
  24. ↑ Mirdehghan, S. A.; Dehghan, M. H.; Mohammadpour, M.; Heidari, K.; Khosravi, M. (2005-05-01). "Causes of severe visual impairment and blindness in schools for visually handicapped children in Iran". British Journal of Ophthalmology. 89 (5): 612–614. doi:10.1136/bjo.2004.050799. ISSN   1468-2079. PMC   1772642 . PMID   15834095.
  25. ↑ Gagrani, Meghal; Garg, Itika; Ghate, Deepta (25 August 2020). "Surgical interventions for primary congenital glaucoma". The Cochrane Database of Systematic Reviews. 2020 (8): CD008213. doi:10.1002/14651858.CD008213.pub3. ISSN   1469-493X. PMC   8094178 . PMID   32816311.
  26. ↑ Roth, Ginny A.; Fee, Elizabeth (2011-03-01). "The Invention of Braille". American Journal of Public Health. 101 (3): 454. doi:10.2105/AJPH.2010.200865. ISSN   0090-0036. PMC   3036681 . PMID   21307377.
  27. ↑ MD, Elias I. Traboulsi (2011-12-01). Genetic Diseases of the Eye, Second Edition. Oxford University Press, USA. ISBN   9780199716975.
  28. ↑ Gogate, Parikshit; Kalua, Khumbo; Courtright, Paul (2009-12-08). "Blindness in Childhood in Developing Countries: Time for a Reassessment?". PLOS Med. 6 (12): e1000177. doi: 10.1371/journal.pmed.1000177 . PMC   2779494 . PMID   19997501.
  29. ↑ "Vision Loss | Kids' Quest | NCBDDD | CDC". www.cdc.gov. 2015-02-07. Retrieved 2015-07-17.
  30. 1 2 Khandekar, Rajiv; Kishore, H.; Mansu, Rabiu M.; Awan, Haroon (2014). "The Status of Childhood Blindness and Functional Low Vision in the Eastern Mediterranean Region in 2012". Middle East African Journal of Ophthalmology. 21 (4): 336–43. doi: 10.4103/0974-9233.142273 . ISSN   0974-9233. PMC   4219227 . PMID   25371641.
  31. ↑ Hussain, A. H. M. Enayet; Ferdoush, Junnatul; Mashreky, Saidur Rahman; Rahman, A. K. M. Fazlur; Ferdausi, Nahid; Dalal, Koustuv (2019). "Epidemiology of childhood blindness: A community-based study in Bangladesh". PLOS ONE. 14 (6): e0211991. Bibcode:2019PLoSO..1411991H. doi: 10.1371/journal.pone.0211991 . ISSN   1932-6203. PMC   6555501 . PMID   31173584.
  32. ↑ "WHO | Priority eye diseases". www.who.int. Archived from the original on March 22, 2006. Retrieved 2015-07-17.
  33. ↑ Hussain, A. H. M. Enayet; Ferdoush, Junnatul; Mashreky, Saidur Rahman; Rahman, A. K. M. Fazlur; Ferdausi, Nahid; Dalal, Koustuv (2019-06-07). "Epidemiology of childhood blindness: A community-based study in Bangladesh". PLOS ONE. 14 (6): e0211991. Bibcode:2019PLoSO..1411991H. doi: 10.1371/journal.pone.0211991 . ISSN   1932-6203. PMC   6555501 . PMID   31173584.
  34. ↑ "VISION 2020". IAPB. Retrieved 12 October 2014.
  35. ↑ "About World Sight Day". The International Agency for the Prevention of Blindness. Retrieved 2022-09-12.

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