An Update on Progress and the Changing Epidemiology of Causes of Childhood Blindness Worldwide

Major Articles An update on progress and the changing epidemiology of causes of childhood blindness worldwide

Lingkun Kong, MD, PhD,a Melinda Fry, MPH,b Mohannad Al-Samarraie, MD,a Clare Gilbert, MD, FRCOphth,c and Paul G. Steinkuller, MDa

PURPOSE To summarize the available data on pediatric blinding disease worldwide and to present current information on childhood blindness in the United States. METHODS A systematic search of world literature published since 1999 was conducted. Data also were solicited from each state school for the blind in the United States. RESULTS In developing countries, 7% to 31% of childhood blindness and visual impairment is avoidable, 10% to 58% is treatable, and 3% to 28% is preventable. Corneal opaciﬁcation is the leading cause of blindness in Africa, but the rate has decreased signiﬁcantly from 56% in 1999 to 28% in 2012. There is no national registry of the blind in the United States, and most schools for the blind do not maintain data regarding the cause of blindness in their students. From those schools that do have such information, the top three causes are cortical visual impairment, optic nerve hypoplasia, and retinopathy of prematurity, which have not changed in past 10 years. CONCLUSIONS There are marked regional differences in the causes of blindness in children, apparently based on socioeconomic factors that limit prevention and treatment schemes. In the United States, the 3 leading causes of childhood blindness appear to be cortical visual impairment, optic nerve hypoplasia, and retinopathy of prematurity; a national registry of the blind would allow accumulation of more complete and reliable data for accurate determination of the prevalence of each. ( J AAPOS 2012;16:501-507)

he definition and categorization of visual impair- worldwide: 39 million were blind, 246 million had low vi- ment was first made by the World Health Orga- sion, and 19 million were children (age 0-14).3,4 Of these, T nization (WHO) in 1972. A revision of this 12 million children (age 0-14) were visually impaired as definition was recommended by the International Classifica- the result of refractive errors, a condition that could be tion of Diseases in 2006.1 The 2010 WHO definition of easily diagnosed and treated, and 1.4 million were visual impairment (Table 1)2 comprises 4 levels of visual irreversibly blind.3 Approximately three-quarters of these function: normal vision (category 0), moderate visual impair- blind children live in developing countries, and up to ment (category 1), severe visual impairment (category 2), 60% of such children die within 1 year of becoming and blindness (categories 3-5). Moderate and severe blind.5 visual impairment are referred to as “low vision.” Low Although childhood blindness is relatively rare and com- vision taken together with blindness is referred to visual prises only 4% of total blindness, the impact is particularly impairment. tragic because children tend to live 40 years longer without According to the updated definition, it was estimated in vision than those with adult-onset vision loss6: the number 2010 that 285 million people were visually impaired of “blind years” experienced by children almost equals the total number of blind years caused by cataract in adults. These years are costly because the blind may have more Author affiliations: aDepartment of Ophthalmology, Baylor College of Medicine, Houston, difficulty securing gainful employment and because they Texas; bBaylor College of Medicine and UT School of Public Health; cThe International require resources from the health care system and their Center for Eye Health, Institute of Ophthalmology, University College, London, United Kingdom families. Childhood blindness also negatively affects neu- Submitted June 14, 2012. robehavioral development, which in turn affects the life Revision accepted September 3, 2012. quality of children and their families. Childhood blindness Correspondence: Paul G. Steinkuller, MD, Department of Ophthalmology, Baylor College of Medicine, 6701 Fannin St, Suite 640, Houston TX 77030 (email: pgsteink@ is a priority not only because interventions are available for texaschildrens.org). prevention but because of the number of blind years in- Copyright Ó 2012 by the American Association for Pediatric Ophthalmology and volved. In this study, we present up-to-date data on various Strabismus. 1091-8531/$36.00 causes of childhood blindness worldwide and in the United http://dx.doi.org/10.1016/j.jaapos.2012.09.004 States.

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Table 1. Revision of categories of visual impairment (ICD-10), Organization/Prevention of Blindness (WHO/PBL) reporting Version for 2010 form, most had different criteria for admissions, and the ages of Best-corrected presenting distance the children varied from 0-15 to 1-18. We excluded children visual acuity .15 years of age according to date of birth. The number of stu- Level of visual Category impairment Worse than Equal to or better than dents in each school for the blind does not reflect the number of blind children in the United States. 0 Mild or none 6/18 3/10 (0.3) Data were analyzed by the same categorization for both world- 20/70 wide and U.S. data according to the anatomic site of the lesion 1 Moderate 6/18 6/60 causing the blindness and according to the stage of development 3/10 (0.3) 1/10 (0.1) at which the causative insult occurred. 20/70 20/200 2 Severe 6/60 3/60 1/10 (0.1) 1/20 (0.05) Results 20/200 20/400 3 Blindness 3/60 1/60a Data were collected from 41 publications representing 33 1/20 (0.05) 1/50 (0.02) countries. Twenty-six were blind school–based studies, 6 20/400 5/300 (20/1200) were population-based, 6 were hospital-based medical re- a 4 Blindness 1/60 Light perception cord reviews, and 3 were key informant studies. All studies 1/50 (0.02) reported using the standardized WHO vision classification 5/300 (20/1200) system; 17 (41%) used the WHO/PBL eye examination 5 Blindness No light perception 8 9 Undetermined or unspecified form (e-Supplement 1, available at jaapos.org). Of the 56 US schools for the blind visually impaired sur- ICD, International Classification of Diseases. aOr counting fingers at 1 meter. veyed, 6 had closed or moved and were unreachable. Sixteen schools (28.6%) from 15 states (Arizona, California, Flor- ida, Kansas, Kentucky, Louisiana, Maryland, Massachu- Methods setts, Minnesota, New Mexico, Oklahoma, Pennsylvania, A systematic search of world literature on childhood blindness South Carolina, Texas, and Washington) supplied data on published since 1999 was conducted. Ovid MEDLINE was a total of 3,070 students. Thirty-nine schools had no data searched for relevant publications from the period 1999-2012 or did not respond. using the following terms: blind, childhood blindness, visual impair- The available data suggest that in economically devel- ment, prevalence, and incidence. The search was limited to human oped countries and regions, such as the United States, studies in English. The list of countries for each World Bank de- Canada, Western Europe, and Japan, the rate of childhood velopment region (http://data.worldbank.org/country) was used blindness is 0.3 to 0.4 per 1,000 children. In the Western to find country-specific articles. Pacific region, the prevalence of childhood blindness is es- The United States does not have a national registry of the blind timated at 0.2 to 0.7 per 1,000; in Asia, 0.9 per 1,000 (range, 0.63-1.09). In undeveloped countries the prevalence can and visually impaired; however, surveys of schools for the blind in 5,9 other countries have become standardized and accepted means of reach 1.2 per 1,000. data collection within the past 20 years, and this methodology was used for US data in the present study. Schools for the blind in the Economic and Geographic Factors United States were contacted at least twice by telephone and sent Economic factors play a major factor role in rates of child- one letter to ascertain whether records were available regarding hood blindness. Of the 33 countries represented in our the causes of vision loss among their students. A total of 64 let- survey, 18 (55%) are classified by the World Bank as ters/data collection sheets were mailed to the 56 schools for the low-income countries, 10 (30%) as medium-income coun- blind from 50 states and Washington, DC, listed at http://www. tries, and 5 (15%) as high-income countries. Nine coun- medicalonline.com/disabled/schools/blindlist.htm. tries from the Africa region are represented, of which 8 On the basis of results from our 1999 study,7 a data collection (89%) are low-income countries, where corneal disease spreadsheet was developed and sent to all responding U.S. schools was found to be the most frequent anatomic cause of visual that had collected diagnosis data upon student enrollment. To en- impairment (28%). In medium- and high-income coun- roll in schools, children must be classified as visually impaired tries, the retina is the major site of visual impairment. when visual impairment (with correction) adversely affects In developing countries a mean of 51% (range, 31%- a child’s learning. This criterion generally includes both blind 70%) of childhood blindness is avoidable; 27% (range, and partially seeing children. We collected data on children con- 10%-58 %), treatable; and 19% (range, 3%-28%), prevent- sidered legally blind, defined as having (1) central visual acuity not able. Among avoidable and treatable causes, retinopathy of .20/200 in the better-seeing eye with corrective lenses (cate- prematurity (ROP) is an emerging etiology. Once consid- gories 2 to 5), or (2) visual acuity .20/200 but accompanied by ered a disease limited to fully industrialized countries, a limitation in the field of vision such that the widest diameter ROP now appears to be most prevalent in middle-income of the visual field subtends an angle no greater than 20 degrees. countries, where mortality rates range from 8 to 60 per None of the schools used the standard World Health 1,000 live births.5,6 Training more ophthalmologists and

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Table 2. Genetic predisposition or developmental stage at which blindness or visual impairment Percentage of populations Hereditary Intrauterine Perinatal Childhood Unclassified WHO region 1999 2012 1999 2012 1999 2012 1999 2012 1999 2012 Africa 16 14 5 4 2 2 47 38 31 48 Americas 30 25 8 12 18 17 12 17 32 17 Eastern Mediterranean 66 25 2 1 2 7 17 43 14 37 European 39 44 6 18 22 2 12 4 22 24 South-east Asian 25 23 3 10 6 4 20 26 46 44 Western Pacific N/A 34 N/A 3 N/A 6 N/A 12 N/A 45 N/A, not available in 1999 data. reinforcing ROP screening programs are important Table 3. Causes of vision loss in students from the schools for VISION 2020 targets for medium-income countries.6 blind in the United States (n 5 3070) Hereditary factors, ranging from 23% to 44% (albinism, 1999 2012 congenital cataracts with family history, retinitis pigmentosa) predominate in the Americas, Europe, Asia, and Western Pa- Diagnosis No % of total No % of total cific region (including Uzbekistan,10 Finland,11 Sri Lanka,12 Cortical visual impairment 515 20 556 18 Cambodia,13 India,12,14-17 and China18-21). Most childhood Optic nerve hypoplasia 166 7 445 15 ROP 320 13 442 14 blindness occurs after the perinatal period, that is, between Optic Atrophy 124 5 211 7 1 month and 15 years of age in the African (38%) and Albinism 140 5 126 4 Eastern Mediterranean (43%) regions (Table 2). This period Coloboma 26 1 86 3 apparently reflects the predominance of corneal opacifica- Glaucoma 43 2 92 3 tion caused by the measles, vitamin A deficiency, and tradi- Retinal detachment, non ROP 21 1 50 2 Leber congenital amaurosis 36 1 56 2 tional eye medicine complex. In Sudan and other African Retinitis pigmentosa 71 3 54 2 22-24 countries, up to 40% of childhood blindness is caused Microphthalmia/Anophthalmia 65 3 58 2 by vitamin A deficiency. Cataract 109 4 72 2 For the last 10 years the WHO has worked with the In- Nystagmus N/A 64 2 ternational Agency for the Prevention of Blindness in the Cone-rod dystrophy 36 1 31 1 Aniridia 58 2 29 1 global initiative “Vision 2020: the Right to Sight.” Since Refractive error N/A 17 1 2004 WHO, in partnership with Lions Clubs International, Congenital infection 7 24 1 has established a global network of 35 childhood blindness Toxoplasmosis 3 11 centers in 30 countries for the preservation, restoration, or Cytomegalovirus 1 3 rehabilitation of sight in children. Improved awareness and Syphilis 0 1 Herpes simplex virus 0 0 treatment of vitamin A deficiency has decreased the per- Rubella 3 0 centage of visual impairment caused by corneal opacity Other 0 9 from 56% in 1999 to 28% in 2012. Vitamin A deficiency unknown 156 1 282 9 and hereditary factors are equal factors (26% and 23%, other 648 25 323 11 respectively) in Asia (Table 2). Trauma-induced blindness Total 2553 100 3070 100 caused by antipersonnel landmine explosions in regions N/A, data not showed separately; ROP, retinopathy of prematurity. affected by civil war involves children as well as adults and has become a significant cause of disability in some Middle Eastern countries, such as Pakistan.25 anophthalmia, cataract (and cataract/cataract surgery com- plications), and nystagmus, each causing 2% to 7% of the total, similar to the 1999 data. Other conditions causing 1% or Causes of Blindness in United States of America less each included cone-rod dystrophy, aniridia, refractive The 16 responding schools maintain excellent rosters of error, and toxoplasmosis. In 282 children (9%) the cause of their students’ causes of blindness. Approximately 10% of blindness was unknown. The retina was the leading anatomic students were recorded with multiple causes (diagnoses), site, causing 30% of impairment (eg, ROP 1 retinal and the authors determined a final cause for each student detachment 1 Leber’s congenital amaurosis 1 retinitis (Table 3). Of the 3,070 US students, the leading causes of pigmentosa 1 cone-rod dystrophy 1 albinism 1 retinal blindness were cortical visual impairment in 556 (18%); coloboma), followed by the optic nerve (23%). Compared optic nerve hypoplasia in 445 (15%), and ROP in 442 with the results of our 1999 study,7 the top three causes of (14%). After these three came optic atrophy, albinism, colo- visual impairment have remained the same. The anterior boma, glaucoma, non-ROP retinal detachment, Leber’s con- segment was the cause of blindness in only 2% of the total, genital amaurosis, retinitis pigmentosa, microphthalmia/ compared with 22% to 51% in the other WHO regions.

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Table 4. Global estimates of visual impairment in children according to anatomic site Site, percentage Number in Optic Whole WHO region Countries with studies sample Cornea Lens Retina nerve Glaucoma globe Africa region Botswana26 162 10.7 22.1 4.3 10.5 7.4 33.8 Southwest Ethiopia27 36 28.0 33.0 N/A 3.0 11.0 19.0 Southwest Nigeria10 30 N/A 26.7 16.7 N/A 20.0 6.7 Nigeria28 45 20.0 N/A N/A N/A 22 N/A Ghana24 201 41.8 22.9 9.0 8.5 15.4 36.8 Kenya, Malawi, Uganda, 1062 19.0 13.1 15.4 12.3 3.0 15.7 Tanzania11 Tanzania, Kilimanjaro29 16 12.5 25.0 0.0 0.0 6.3 0.0 Ethiopia22 295 62.4 9.2 2.4 9.8 1.7 4.7 Total or average 1847 28 22 8 7.3 10.9 16.7 Region of the Americas Chile30 217 10.6 9.2 47 12 8.3 8.8 Mexico31 144 2.1 1.4 47.9 17.4 14.6 9.0 Brazil32 3210 0.5 6.7 36.3 11.6 7.0 10.5 Total or average 3571 4.4 5.8 42.1 13.7 10 9.4 Eastern Mediterranean region Iran12 211 4.3 7.1 62.6 7.1 N/A 17.5 Yemen14 93 13.3 20 13.3 11.1 17.8 N/A Pakistan25 50 8.0 N/A 24.0 12.0 N/A 32.0 Sudan15 40 40.0 12.5 7.5 2.5 2.5 2.5 Total or average 394 16.4 13.2 26.9 8.2 10.2 17.3 European region Izmir, Turkey23 148 N/A 20.2 25.0 N/A N/A N/A Uzbekistan16 506 5.7 29.1 30.2 5.7 4.7 15.4 Netherlands17 800 N/A 16.3 N/A N/A 0.04 N/A Finland33 431 N/A 13 31 23 N/A N/A Poland34 3000 N/A 14.1 8.1 21.7 6.42 N/A UK35 439 2 5 29 28 3 7 Total or average 6112 3.9 15.2 29 22.4 3.9 8.5 South-east Asian region Myanmar36 202 43.6 14.4 7.4 4.0 5.4 21.2 Indonesia18 477 16.1 16.4 18.9 5.0 1.7 35.9 Indonesia, Wiyata Guna 165 17.6 13.3 26.0 6.1 N/A 32.7 School19 Sri Lanka20 206 7.8 10.9 35.9 10.9 3.1 22.4 South India21 891 13.7 14.1 20.3 4.4 1.9 41.4 Southern India13,30 305 20.5 7.9 23.9 4.9 6.7 18.5 Maharashtra, India37 1778 22.2 6.0 11.2 N/A 41.3 N/A Northeastern India38 258 36.4 10.9 5.8 5.4 1.2 36.1 North India39 650 21.7 10.9 15.1 10.6 4.9 27.4 Nepal40 259 35.8 12.6 20.4 13.0 13.3 Bangladesh41 1935 26.6 32.5 12.7 8.0 4.3 13.1 Total or average 7126 23.8 13.6 17.9 7.2 7.8 26.2 Western Paciﬁc region East China42 385 N/A 27.5 22.5 14.9 N/A 15.2 China43 1131 4.4 18.8 24.9 13.6 9.0 25.5 Hong Kong, China44 82 7.3 14.6 47.6 14.6 12.2 2.4 Cambodia45 62 25.8 27.4 21.0 3.2 3.2 17.7 Fiji46 81 1.9 15.5 45.3 9.4 N/A 13.2 Mongolia47 56 7.1 34 12.5 12.5 3.8 14 Malaysia48 448 8.5 17.2 33.0 7.6 7.6 19.2 Vietnam49 411 10.9 15.1 24.6 10.2 5.4 29.4 Total or average 2685 9.4 21.3 28.9 10.8 6.9 17.1 N/A, not available; WHO, World Health Organization.

Anatomic Sites of Blinding Disease of childhood blindness worldwide, the leading conditions Data on causes of world childhood blindness were summa- are cataract, ROP, and glaucoma. Data from high- rized according to anatomic site of the lesion causing blind- income countries were limited; however, available infor- ness and grouped into the six WHO regions (Table 4).10-49 mation indicates no major changes in prevalence over the The leading anatomic sites of childhood blindness in the past decade (Table 4). world (Table 5) are retina (eg, ROP, retinal and macular dystrophy, retinitis pigmentosa), followed by whole globe (microphthalmia/anophthalmia), cornea, and lens (cataract Discussion with and without surgery). Other causes, including con- Several countries maintain efﬁcient national registries of genital infectious disease, are rare. Of the treatable causes the blind and visually impaired, including Canada, the

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Table 5. Anatomic site of lesion causing blindness and visual and many blind children have multiple disabilities, making impairment by WHO region accurate vision testing difficult. The prediction of inci- Leading causes dence is even more difficult because it requires longitudinal studies or efficient data entry systems. According to the WHO region 123 Australian Childhood Vision Impairment Register,51 vi- Africa region Cornea Lens Whole globe sion impairment affects 1 in 2,500 children; it is estimated Region of the Americas Retina Optic nerve Glaucoma Eastern Mediterranean Retina Whole globe Cornea that 4 of every 10,000 children born in Australia will be region diagnosed with severe vision impairment or blindness by European region Retina/CVI Optic nerve Lens his or her first birthday. South-east Asian region Whole globe Cornea Retina In the United Kingdom, the most predominant disor- Western Pacific region Retina Lens Whole globe ders were cortical visual impairment (CVI), retinal disor- CVI, cortical visual impairment; WHO, World Health Organization. ders (including ROP), and disorders of the optic nerve (including optic nerve hypoplasia), affecting 48%, 29%, United Kingdom (visual impairment, blindness, and partial and 28% of all children, respectively.52 Children with sight registers [ages 0-15]) Finland (Finnish Register of low birth weight were significantly more likely to have Visual Impairment), Kuwait (The Registry of the Visual CVI. According to Rahi52 and our unpublished data, chil- Disability Committee), and Australia (Australian Child- dren with low birth weight (\2500 g) were significantly hood Vision Impairment Register [ages 0-18]); however, more likely to have CVI than those of normal birth weight. there is no standardized worldwide data collection system. Screening and treatment can prevent blindness caused by The age range for data collection varies from 0 to 14 ROP in these children, but it cannot prevent blindness (WHO definition of childhood) to 0-16 (United Nations from CVI. To prevent blindness secondary to CVI, more Children’s Fund or 0 to 18). The WHO/PBL eye examina- emphasis must be placed on prevention through improved tion form is commonly used worldwide. perinatal care, prevention of premature birth, and if possi- In our study, 78% of the data sources were blind school- ble, prevention of intraventricular hemorrhages. The rate or hospital-based; 15%, population-based ocular disease of CVI in the United States from this study is lower than prevalence surveys; and 7% (3) key informant studies. the data from United Kingdom. As mentioned previously, The population-based studies seldom involved enough our data were from children who attended schools for the children to yield meaningful data.27 Key informant studies, blind. Children with CVI also tend to have multiple dis- a study method initially developed for use in surveys of abilities and many of were not enrolled at these institutions. psychosis and epilepsy, recently has gained popularity in More accurate data would require establishment of a na- the estimation of population prevalence of childhood tional registry for blindness and visual impairment. blindness. Surveys of schools for the blind still function In conclusion, despite study limitations, WHO criteria as an affordable and convenient way of assessing the causes and classification used in conjunction with demographic of childhood blindness; however, there are limitations. data, blind school–based studies reveal marked regional Children living in remote areas may be under- and intraregional differences in the prevalence and causes represented in all the countries. In India, approximately of blindness and severe visual impairment worldwide. 5% of visually impaired school-aged children have been The 3 leading causes of childhood blindness and severe enrolled for education (www.bpaindia.org). In the United visual disability in the United States identified by this States only about 13% of legally blind children attend study were CVI, ROP, and optic nerve hypoplasia, the schools for the blind.50 Many blind or severely visually im- same 3 as in 1999. This result may reflect some case paired American children live at home and attend their selection to conditions for which there is no adequate pre- local schools with assistance from itinerant professional vention, for example, prematurity. It may also mean that, educators of the disabled. According to a 2009 report by as a fully developed country, public health issues such as the American Printing House for the Blind, there were malnutrition and infectious disease do not represent a sig- 59,355 legally blind children (through age 21) enrolled in nificant factor in childhood blindness and visual impair- elementary and high school in the United States who ment in the United States. Most childhood blindness in were eligible to receive free reading matter in Braille, large the United States and the rest of the industrialized world print, or audio format. Approximately 8,000 (13%) were is due to perinatal and hereditary factors; in the Americas, from schools for the blind. Thus our data, based on blind Europe, Asia, and Western Pacific region to hereditary children in U.S. institutions, is not comprehensive. In ad- factors; and in Africa to disease during childhood. Retinal dition, admission criteria vary among schools; for example, disease causes most childhood blindness in the United age in these studies varies from 0-14 to 0-18. Moreover, States and other fully developed countries, compared school studies do not uniformly report data according to with corneal opacities in Asia and Africa. More detailed WHO definitions. and accurate data from schools for the blind in the United Childhood blindness is relatively rare compared with States could be obtained by a unified survey using the stan- adult blindness, accounting for only 4% of total blindness dardized WHO/PBL format or by creation of a national worldwide.3 Population-based surveys are very expensive, registry for blindness.

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