LEADING CAUSES OF BLINDNESS WORLDWIDE

ROODHOOFT J.M.J.*

SUMMARY KEY-WORDS The main causes of blindness and visual disabili- Blindness, visual disability, avoidable ties, as described in documents published by the blindness, non avoidable blindness, World World Health Organization (WHO), are discussed. Health Organization RÉSUMÉ MOTS-CLÉS Les causes principales de la cécité et de la déficience Cécité, déficience visuelle, cécité évitable, visuelle sur base de documents établis par l’Organi- cécité non - évitable, Organisation Mondiale sation Mondiale de la Santé (OMS), sont discutées. de la Santé SAMENVATTING De voornaamste oorzaken van blindheid en slecht zien worden besproken op basis van documenten die gepubliceerd worden door de Wereldgezondheidsor- ganisatie.

zzzzzz * Department of Ophthalmology, Algemeen Ziekenhuis Sint-Jozef, Turnhout, Belgium. received: 14.11.01 accepted: 05.01.02

Bull. Soc. belge Ophtalmol., 283, 19-25, 2002. 19 One of the main functions of the World Health is no prevention for (5). Cataract sur- Organization (WHO) is to give worldwide guid- gery, including the implantation of an intra-oc- ance in the field of health (35). Blindness is de- ular , may restore the to near fined as visual acuity of less than 3/60 (0.05) normal levels (23). The cost-effectiveness of or corresponding visual field loss (a field less cataract surgery has been demonstrated world- than 10°) in the better eye with best possible wide. A real restoration of the vision and a real correction. This corresponds to loss of walk- improvement in the quality of life is obtained; about vision. Low vision corresponds to visual furthermore adults can return to their work (15). acuity of less than 6/18 (0.3) but equal to or That is why the volume of cataract surgery has better than 3/60 (0.05) in the better eye with increased worldwide (22). the best possible correction (43). The number of cataract operations per million There are currently 45 million people blind and population per year (Cataract Surgical Rate) 135 million people with low vision. The global varies from country to country and even within blindness prevalence was estimated to be 0.7 countries, ranging from an estimated 5000 in % in 1990. Of this global burden of blindness the USA to approximately 200 in the whole of 90 % is born by developing countries and 80 Africa (7). In Europe cataract surgery with im- % is avoidable (preventable or treatable) with plantation of an intra-ocular lens is done rou- applying existing knowledge and technology. tinely. The intra-ocular lens is available in Bel- Blindness is also more prevalent in the older gium at a prize of € 157.66 (3). It has been age groups, largely as a result of non-commu- estimated that India has 11.9 million people nicable diseases. The number of blind increas- in urgent need of cataract surgery (2). In India es every year by 2 million and is expected to only 11% of all cataract surgery is done with double by the year 2020 (6, 17, 25, 40). implantation of an intra-ocular lens, which is In order to drastically reduce the global bur- available at a price of US$ 10 (25). China has den of blindness the WHO launched an initia- about 18% of the world’s blind and each year tive to combat and eliminate avoidable blind- an estimated 450 000 become blind. Where ness. The name of that initiative is VISION 2020: several years ago was the main cause THE RIGHT TO SIGHT. Five conditions have of blindness, today cataract accounts for ap- been identified as immediate priorities within proximately 50% of China’s blind (36). In Af- the framework of VISION 2020. These are ca- rica and China less than 10% of the cataract taract, trachoma, , and refrac- patients receive surgical treatment. It is cer- tive errors and low vision (17, 23). tain that in the poorer countries huge efforts will be necessary in order to provide cataract sur- gery with lens implantation to all those in need. AVOIDABLE BLINDNESS The WHO estimates the number of cataract op- erations in 2000 to be 12 million and predicts The three main causes of that in 2020 32 million cataract operations will blindness be performed. This increase in volume of ca- taract surgery will be a consequence of the in- Cataract, trachoma and are respon- creased number of elderly people and the world- sible for more than 70 % of the global blind- wide increase in services (particularly in the de- ness (34, 40). veloping countries) (7, 22, 29, 40).

Cataract Trachoma

Cataract, a loss of the normal transparency of Trachoma is responsible for 6 million blinded the crystalline lens due to an opacity, is respon- people or 15% of world’s blindness. There are sible for half of all blindness worldwide, and is some 146 million cases of active disease due largely related to the ageing process (the older to infection with Chlamydia trachomatis. Re- a person, the greater the chance of developing peated eye infections cause and hence a cataract) all over the world (4). Therefore ca- corneal blindness. Trachoma is common in ar- taract is an universal cause of blindness. There eas of the world that are socio-economically de-

20 prived of basic needs in housing, health, water Other causes of blindness and sanitation. There is no medical treatment once the has lost its transparency. Tra- Childhood blindness choma can be prevented trough the implemen- Childhood blindness is a priority area, consid- tation of the ’’SAFE strategy’’: surgery for tri- ering the number of years the visual handicap chiasis, azithromycin (antibiotic treatment), fa- plays a role, the high frequency of developmen- cial cleanliness and environmental improve- tal anomalies and the fact that many of the con- ment (hygiene) (8). Trachoma occured also in ditions associated with blindness in children are Belgium before world war I and disappeared also causes of child mortality (9). Each year, even before the antibiotics were discovered due an estimated half a million children go blind, to better environmental and hygienic condi- mostly in the poorest countries of Asia and Af- tions. It should therefore be understood that tra- rica, of whom up to 60% die in childhood. Sev- choma will only disappear if all four elements enty-five per cent of these children suffer from of the treatment are implemented. The WHO , which causes night blind- predicts that trachoma will disappear as a blind- ness, , an increased suscep- ing disease (1, 13, 14, 17, 27, 40). tibility to ocular infections and a higher risk of dying from infections due to an impaired im- Glaucoma mune system. Vitamin A deficiency is consid- ered to be the main cause of childhood blind- Glaucoma is responsible for 5.2 million blind ness. There are still 78 countries that have chil- people or 13.50 % of the total burden of world dren with vitamin A deficiency (41). Malnutri- blindness and is therefore considered to be the tion is a contributing factor in half of all child- third largest cause of blindness worldwide. Ac- hood deaths (32). Vitamin A deficiency can be cording to Thylefors and Négrel (24) glauco- corrected by supplementation of vitamins or by ma is not a single disease but rather a group of teaching the people to change their diet. An- disorders that have common features such as other way of dealing with childhood blindness cupping and atrophy of the , charac- is to take care that all children get the neces- teristic visual field loss and often an increased sary vaccinations at the right time. The combi- intra-ocular pressure. Glaucoma is more com- nation of measles vaccination and vitamin A mon in populations of African of Asian heri- supplementation has been one of the major tage. There is no preventive treatment for glau- success stories in reducing death from infec- coma, but visual loss can be avoided if glau- tious diseases. Worldwide, corneal scarring is coma is detected and treated at an early stage. the single most important cause of avoidable All people should be instructed about this dis- paediatric blindness, followed by cataract and ease because people who are aware of this dis- of prematurity (ROP). ROP occurs ease are more motivated to have them screened in babies who survive very low birth weight and for this condition and all people should have is related to the response of immature retinal their eye pressure checked regularly (certainly vasculature to high oxygen exposure. The crea- when there is a predisposition for glaucoma). tion of neonatology units in the western world It is an example of health education thereby re- but also in larger cities of developing countries ducing and reducing cost of has increased dramatically the survival of pre- eye care. In Africa at least half of eyes are al- mature babies. However these children need ready blind at first presentation (13). careful ophthalmologic monitoring in order to Tonometry alone does not detect all cases of allow the early detection and treatment of ROP glaucoma, therefore it is to be hoped that new and thus avoid its dramatic complications (11). techniques for the early detection of glaucoma Onchocerciasis (river blindness) will improve the outcome of this disease (23, 40). Onchocerciasis is caused by Onchocerca vol- In Belgium glaucoma, and vulus, a parasitic worm that lives for up to 14 trauma are the main causes of avoidable blind- years in the human body. Each adult female ness. worm produces millions of microfilariae that mi-

21 grate throughout the body and give rise to a va- sual handicap. Loss of vision and blindness in riety of symptoms: serious visual impairment persons with diabetes is the leading cause of due to an intense inflammatory reaction caused blindness and visual disability in adults in eco- by the dead of the microfilaria in the eye; le- nomically developed societies, such as Bel- sions of the skin; lymphadenitis and general de- gium. India has the highest number of diabe- bilitation. tics in the world. In Europe about 22.5 million There are 120 million people worldwide who adult people, 5% of the population, are diabetic are at risk of onchocerciasis. A total of 18 mil- and worldwide an estimated 150 million people. lion people are infected of whom 99% are in The WHO predicts a rise to 300 million by 2025 Africa (13). Of those infected, over 6.5 million due to ageing, unhealthy diets, the fact that un- suffer from dermatitis and 270 000 are blind. healthy food is frequently cheaper, obesity and Onchocerciasis is often called ’’river blindness’’ a sedentary lifestyle. because this filarial disease may cause blind- Most of the direct costs of diabetes result from ness and because the black flies that transmit its complications. And, if the increase of dia- the disease breed on rapid flowing streams. On- betes and its complications occurs as predict- chocerciasis may start one year after a bite of ed by the WHO, the financial implications for the black fly (39). the health services will be disastrous (37). Loss Onchocerciasis constitutes a serious obstacle of vision due to diabetic retinopathy can often to the socio-economic development, as many be prevented by regular eye examinations and people do not want to live next to these rapid timely intervention with laser treatment or sur- flowing streams for fear of becoming blind be- gery (19, 23, 40). Screening of people with dia- cause of infection. And these rapid flowing betes is cost effective. A recent study has dem- streams turn the grounds in the vicinity into fer- onstrated that diet, good metabolic control, as- tile areas. If these fertile grounds are not used siduous treatment of arterial hypertension, cor- for agriculture that means that large parts of rection of hyperlipidemia and a less sedentary these countries are not contributing to the eco- life style can also delay the onset and progres- nomy and welfare. sion of diabetic retinopathy (20, 21). In Bel- The treatment of this disease is: gium diabetic patients have access to all the 1) by eliminating the black flies through ap- necessary care to prevent the complications of plication of selected insecticides through aerial diabetic retinopathy. In developing countries spraying of breeding sites in fast-flowing rivers. such care is inaccessible to the majority of the 2) by killing the larval worms with Ivermectin, population. a safe and effective medication (one dose a year is distributed free of charge to all those who Ocular injuries need it) (40). The WHO hopes that this disease will disap- Ocular trauma is a common cause of visual loss pear before the year 2010 and that will hap- and is known to be the most common cause of pen at a cost of less than US$ 1 per year for unilateral loss of vision. Each day eye injuries each protected person. The success of the con- occur that cause suffering, medical costs and trol of onchocerciasis in eleven West African one or more days of restricted activity. In countries proves that disease control can be an developing countries, the problem of injuries is economic investment with exceptionally high more severe as there is often a delay before returns (27, 39). these eye injuries are handled in the proper way. Ocular trauma is the cause of bilateral Diabetes mellitus blindness in more than one million people (16). Ocular trauma can be prevented by risk appre- Diabetes is a disease that in the long-term may ciation and avoidance, widespread wearing of lead to complications such as blindness, kid- high-performance spectacles or protective ney failure and limb amputation, as well as to goggles, appropriate occupational processing heart disease and stroke (31). After 15 years and shielding, extension of on-the-job safety to of diabetes, approximately 2% of people be- the home environment and the application of come blind while about 10% develop severe vi- modern principles of surgical salvage (12).

22 Leprosy 23). Provision of low vision care to enhance the use of residual vision of people with ARM or Leprosy is a chronic infection caused by Myco- other eye diseases is one of the five objectives bacterium Leprae (Hansen - 1873) that main- of VISION 2020, an ambitious program of the ly affects the skin, the peripheral nerves, the WHO to help those most in need of visual re- mucosa of the upper respiratory tract and also habilitation (33, 38). the eyes. In Europe the prevalence of leprosy declined steadily since the 14th century (26, 27). At the beginning of 2000, the prevalence CONCLUSION rate at the global level was around 1.25/10000 There is real hope that the mass of blindness and the number of leprosy patients was report- and visual impairment will decrease consider- ed as about 640.000. The most affected area ably due to steady efforts of the WHO and its is India. It has been estimated that there are partners. That is true for blindness due to some 250 000 blind from the disease. The cataract, and infectious disease. WHO ensures that all leprosy patients have free There is need for more research to fight diseas- and equal access to Multiple Drug-Therapy, the es such as glaucoma and ARM. In cases of di- most modern treatment available, that cures abetes mellitus prevention through treatment leprosy within twelve months. The WHO elim- of arterial hypertension, education, a less sed- ination strategy has led to an 85% reduction entary life and a better diet may improve dras- of leprosy prevalence over 15 years: Multiple tically patients’ quality of life. Drug-Therapy had cured more than 10 million patients by the end of 1999. There is real hope REFERENCES that leprosy will disappear as a cause of blind- ness, although there are momentarily 24 coun- (1) BAILEY R., LIETMAN T. − The SAFE strategy tries where leprosy remains a public health prob- for the elimination of trachoma by 2020: will lem (30, 42). it work? Bull. W.H.O., 2001; 79: 233 - 236. It is not really understood why con- (2) BACHANI D., MURTHY G.V., GUPTA K.S. − tinues to progress in leprosy patients that show Rapid assessment of cataract blindness in In- no sign of active infection with Mycobacterium dia. Indian J. Public Health, 2000; 44: 82-9. Leprae. (3) BELGISCH STAATSBLAD 1 Februari 1997. (4) BRIAN G., TAYLOR H. − Cataract Blindness - challenges for the 21st century. Bull. W.H.O., NON AVOIDABLE 2001; 79: 249-256. BLINDNESS (5) CONGDON N.G. − Prevention strategies for age related cataract: present limitations and future Age-related (ARM) is the most possibilities. Br. J. Ophthalmol., 2001; 85: common disorder in the group of non-avoid- 516-520. able causes of visual loss (28). It is also an uni- (6) CUNNINGHAM Jr. E.T., LIETMAN T.M., versal cause of visual loss. Hogan sounded a WHITCHER J.P. − Blindness: a global priority warning note 30 years ago that the increase in for the twenty-first century. Bull. W.H.O., 2001; the prevalence of ARM due to aging of the po- 79: 180. pulation will become a major economical and (7) FOSTER A. − Cataract and ’’VISION 2020 - the social problem (10). More than 25% of people right to sight’’ initiative. Brit. J. Ophthalmol., over 80 years may have the condition. There 2001; 85: 635-637. (8) FRASOR-HURT M., BALY R.L., KUSOUS S., is not yet a preventive treatment that has a sig- − nificant impact on blindness due to ARM. There MAYBEY D., FALL H., MAYBEY D.C.W. Efficacy of oral azithromycin versus topical te- is no therapy for the dry form of the late stage tracycline in mass treatment of endemic tracho- of ARM. There are limited forms of therapy with ma. Bull. WH.O., 2001; 79: 632-640. the objective of limiting the visual loss by de- (9) GILBERT C., FOSTER A. − Childhood blind- stroying new vessels arising in the (the ness in the context of VISION 2020 - The Right wet form of the late stage of ARM). That is why to Sight. Bull. W.H.O., 2001; 79: 227-232. there is a need for more effort to find a way to (10) HOGAN M.J. − Bruch’s membrane and disea- preserve a healthy macula in the elderly (18, se of the macula: role of elastic tissue and col-

23 lagen. Trans. Ophthalmol. Soc. UK., 1967; 87: (28) WORLD HEALTH ORGANIZATION − Blindness 113-161. and Visual Disability: Other Leading Causes (11) HOYT C.S., GOOD W.V. − The many challen- Worldwide Fact Sheet No 144, Geneva: Fe- ges of childhood blindness. Br. J. Ophthalmol., bruary 1997, W.H.0., unpublished document 2001; 85: 1145-1146. available at http:www.who.int/inf-fs/en/ (12) KEENEY A.H. − Prevention of Eye Injuries. In: fact144.html Freeman H.M., Ocular Trauma. Appleton-Cen- (29) WORLD HEALTH ORGANIZATION − Global ini- tury-Crofts, New York, 1979; 377-383. tiative for the elimination of avoidable blind- (13) LEWALLEN S., COURTRIGHT P. − Blindness ness - vision 2020 launched in English speaking in Africa: present situation and future needs. Africa, South Africa set to eliminate cataract Br. J. Ophthalmol., 2001; 85: 897-903. blindness within the next five years. Press Re- (14) LIETMAN T., FRY A. − Can we eliminate tracho- lease WHO/27, Johannesburg, South Africa: ma? Br. J. Ophthalmol., 2001; 85: 385-387. 19 April 2000, W.H.O., document PR-2000- (15) MAURICE J. − Restoring sight to the millions - 27 available at http:www.who.int/inf-pr-2000/ the Aravind way. Bull. W.H.O., 2001; 79: 270- en/pr2000-27.html 271. (30) WORLD HEALTH ORGANIZATION − Leprosy: (16) NEGREL A.D., THYLEFORS B. − The global global situation. Wkl. Epidemiol. Rec. 2000; impact of eye injuries. Ophthalmic Epidemiol., 75: 226-231. 1998; 5: 143-169. (31) WORLD HEALTH ORGANIZATION OFFICE OF (17) RESNIKOFF S., PARARAJANSEGARAM R. − HEALTH COMMUNICATIONS AND PUBLIC RE- Blindness prevention programmes: past, pre- LATIONS − Diabetes Mellitus Fact Sheet No sent, and future. Bull. W.H.O., 2001; 79: 222- 138, Geneva: November 1999, W.H.O., un- 226. published document available at http:www. (18) ROODHOOFT J. - No efficacious treatment for who.int/inf-fs/en/fact138.html. age-related . Bull. Soc. (32) WORLD HEALTH ORGANIZATION OFFICE OF belge Ophtalmol., 2000; 276: 83-92. HEALTH COMMUNICATIONS AND PUBLIC RE- (19) SAXENA S., JALALI S., MEREDITH T.A., HO- LATIONS − Reducing mortality for major child- LEKAMP N.M., KUMAR D. - Management of hood killer diseases. WHO Fact Sheet No. 178, diabetic retinopathy. Indian J. Ophthalmol., Geneva: 1997, W.H.O., unpublished document 2000; 48: 321-30. available at http:www.who.int/inf-fs/en/ (20) SCHEEN A.J. - Treatment of diabetes in pa- fact178.html. tients with severe obesity. Biomed. Pharma- (33) WORLD HEALTH ORGANIZATION OFFICE OF cother., 2000; 54: 74-9. INFORMATION − Blindness and Visual Disa- (21) STRATTON I.M., KOHNER E.M., ALDINGTON bility: part 5: seeing ahead: Projections into the S.J., TURNER R.C., HOLMAN R.R., MANLEY Next Century. Fact Sheet No 146. Geneva: Fe- S.E., MATHEWS D.R. − UKDPS 50: risk fac- bruary 1997, WHO, unpublished document tors for incidence and progression of retinopa- available at: http:www.who.int/inf-fs/en/ thy in Type II diabetes over 6 years from dia- fact146.html. gnosis. Diabetologia, 2001; 44: 156-63. (34) WORLD HEALTH ORGANIZATION OFFICE OF (22) TAYLOR H.R. − Cataract: how much surgery INFORMATION − Blindness and Visual Disa- do we have to do? Br. J. Ophthalmol., 2000; bility: part 2: Major Causes Worldwide. Fact 84:1-2. Sheet No 143, Geneva: February 1997, W.H.O., (23) TAYLOR H.R., KEEFFE J.E. − World blindness: unpublished document available at: http: a 21st century perspective. Br. J. Ophthalmol., www.who.int/inf-fs/en/fact143.html. 2001; 85: 261-266. (35) WORLD HEALTH ORGANIZATION OFFICE OF (24) THYLEFORS B., NÉGREL A.-D. − The global INFORMATION − The World Health Organiza- impact of glaucoma. Bull. W.H.O., 1994; 72: tion. Fact Sheet No 126, Geneva: August 1996, 323-326. W.H.O., unpublished document available at (25) THYLEFORS B. − Avoidable blindness. Bull. http:www.who.int/inf-fs/en/fact126.html. W.H.O., 1999; 77: 453. (36) WORLD HEALTH ORGANIZATION OFFICE OF (26) WITCHER J.P.,SRINIVASAN M. − Leprosy - a PRESS AND PUBLIC RELATIONS − Blindness new look at an old disease. Br. J. Ophthal- as a Public Health Problem in China. Fact Sheet mol., 2000; 84: 809 - 812. No 230. Global initiative for the elimination of (27) WITCHER J.P., SRINIVASAN M., UPADHYAY avoidable blindness (Vision 2020): blindness M.P. − Corneal blindness: a global perspecti- as a public health problem in China. Geneva: ve. Bull. W.H.O., 2001, 79: 214-221. September 1999, W.H.O., unpublished docu-

24 ment available at http:www.who.int/inf-fs/en/ WORLD HEALTH ORGANIZATION EXPANDED fact230.html. PROGRAMME ON IMMUNIZATION, WORLD (37) WORLD HEALTH ORGANIZATION OFFICE OF HEALTH ORGANIZATION DIVISION OF NU- PRESS AND PUBLIC RELATIONS − The costs TRITION, WORLD HEALTH ORGANIZATION of diabetes Fact Sheet No 236: The costs of DIVISION OF DIARRHOEAL AND ACUTE RES- diabetes: World Diabetes Day - 14 November PIRATORY DISEASE CONTROL − Using im- 1999, Geneva: 1999, W.H.O., unpublished munization contacts as the gateway to elimi- document available at http:www.who.int/inf- nating vitamin A deficiency a policy document. fs/en/fact236.html. Document no. WHO/EPI/GEN/94.9 Rev.1 (Un- (38) WORLD HEALTH ORGANIZATION PRESS OF- published), Geneva: 1995, W.H.O., available FICE − Control of major blinding diseases at http:whqlibdoc.who.int/hq/1994/ and disorders: Vision 2020: the Right to WHO_EPI_GEN_94.9_Rev.1pdf. Sight, WHO Fact Sheet No 214, Geneva: Fe- (42) WORLD HEALTH ORGANIZATION STRATEGY bruary 2000, W.H.O., unpublished document DEVELOPMENTANDMONITORINGFORERA- available at http:www.who.int/inf-fs/en/ DICATION AND ELIMINATION TEAM. Guide to fact214.html. eliminate leprosy as a public health problem. (39) WORLD HEALTH ORGANIZATION PRESS OF- Document no. WHO/CDS/CPE/CEE/2000.14, FICE − Vision 2020: the Right to Sight: On- Geneva: 2000, W.H.O. available at http:whq- chocerciasis (river blindness). WHO/OMS Fact libdoc.who.int/hq/2000/WHO_CDS_CPE_ Sheet No. 95 (revised) Onchocerciasis (river CEE_2000.14.pdf. blindness); Geneva: February 2001, W.H.O., (43) WORLD HEALTH ORGANIZATION STUDY document available at http:www.who.int/inf- GROUP ON THE PREVENTION OF BLIND- fs/en/fact 95.html NESS - The prevention of blindness - report of (40) WORLD HEALTH ORGANIZATION PROGRAM- a WHO Study Group. Technical report series ME FOR THE PREVENTION OF BLINDNESS N° 518, Geneva: 1973, W.H.O., available at AND DEAFNESS - Global initiative for the eli- http:whqlibdoc.who.int/trs/WHO_ TRS_518.pdf. mination of avoidable blindness. World Health Organization Programme for the Prevention of Blindness and Deafness. Document no.: WHO/PBL/97.61 Rev.1; Geneva: 1997, W.H.O., zzzzzz unpublished document available at http: whq- Address for correspondence: libdoc.who.int/hq/1997WHO_PBL_97.61_Rev.1.pdf. Jan Roodhooft, M.D. (41) WORLD HEALTH ORGANIZATION PROGRAM- Steenweg op Merksplas 44 ME FOR THE PREVENTION OF BLINDNESS, B - 2300 Turnhout

25