S Afr Optom 2005 64 (2) 44 − 54 Prevalence and causes of low vision and blindness worldwide AO Oduntan* Department of Optometry, University of Limpopo, Private Bag X1106, Sovenga, 0727 South Africa <[email protected]> Abstract Introduction A recent review of the causes and prevalence There are many low vision and blind people of low vision and blindness world wide is lack- worldwide, and there is a considerable amount of ing. Such review is important for highlighting data available on the prevalence of low vision and the causes and prevalence of visual impairment blindness in many parts of the world. The data, in the different parts of the world. Also, it is however, vary significantly from one continent to important in providing information on the types another. In 1995, the World Health Organization and magnitude of eye care programs needed in (WHO) Task Force on data on blindness estimated different parts of the world. In this article, the that there were 37.1 million blind people world- causes and prevalence of low vision and blind- wide, indicating a global prevalence of 0.7 percent1. ness in different parts of the world are reviewed According to that report, the prevalence values and the socio-economic and psychological range from 0.3% in the developed countries to implications are briefly discussed. The review 1.4% in Sub-Saharan African countries. The preva- is based on an extensive review of the litera- lence of visual impairment is expected to be higher ture using computer data bases combined with in the developing countries due to the low level of review of available national, regional and inter- health care services in many of the countries. It has national journals. Low vision and blindness are subsequently been reported that 110 million people more prevalent in the developing countries than have severely impaired vision, hence are at great in the developed ones. Generally, the causes risk of becoming blind2. More recently, follow- and prevalence of the conditions vary widely in ing a review of available data, Watkins3 estimated different parts of the world and even within the that there were about 40 million people (0.7%) same country. World wide, cataract is the most who are blind worldwide and predicted an annual common cause of blindness and low vision increase of about two million. In both developing among adults and elderly. Infectious diseases and developed countries, the prevalence of low such as trachoma and onchocerciasis result- vision and blindness increases with age, particularly ing in low vision and blindness are peculiar among people over 60 years of age. This is due to to Africa, Asia and South America. Hereditary age-related eye diseases such as cataract, macular and congenital conditions are the most common degeneration et cetera, which have high prevalence causes of low vision and blindness among chil- among this age group. A review of available data on dren worldwide. prevalence of low vision and blindness in various regions of the world is presented below. Keywords: Visual impairment, blindness, low vision, partial sight, prevalence, cataract, Africa childhood blindness. It is generally known that Africa has a high rate *BOptom (Hons) PhD Received 10 January 2005; revised version accepted 18 June 2005 44 The South African Optometrist − June 2005 Prevalence and causes of low vision and blindness worldwide of blindness. It has been estimated that approxi- matous infections and trachoma, which occurred mately 1% of Africa’s population is blind4 and in 0.4% and 0.3% of the population respectively. a higher prevalence has been estimated for Sub- In another study15 among the Turkana tribe in the Saharan Africa1. The most common causes of North West of Kenya, the major causes of blind- low vision and blindness among adults are cata- ness among those below 35 years of age were cor- ract, corneal and retinal diseases. About half of neal diseases from xerophthalmia and trachoma. the blindness is due to cataract alone5, 6. Women Among those over 45 years, cataract was the main accounted for approximately 60% of the blind; an cause of blindness. In a population based sur- age-adjusted prevalence of blindness in women vey16 in the Hammer tribe of Ethiopia, blindness was 1.39 times higher than in males5, 6. A national occurred in 1.9% of the population. Among those blindness prevalence of 0.7% was reported for aged 40 years and over, 1% of the men and 13% Ghana based on hospital data7. A subsequent of the women were blind. Women and men with population-based survey8 on the prevalence of low vision or blindness comprised 30% in that age major blinding disorder in the Wenchi district in stratum. The survey identified cataract as the major central Ghana estimated the prevalence of blind- cause of blindness. A similar survey in the Jimma ness among those 30 years and older to be 1.7%, Zone of Ethiopia17, found cataract (56.8%), refrac- and additionally, the prevalence of low vision was tive error (28.8%), and corneal opacity (12.8%) 2%. That study showed that cataract (62.5%) was to be major causes of low vision. Also, cataract the most common cause of blindness in individuals and aphakia (52.4%), corneal opacity and phthisis aged 30 years and older. Other common causes of bulbi (25.4%) and glaucoma (9.5%) featured sig- blindness identified in that study were onchocer- nificantly as major causes of blindness. ciasis (12.5%), non-trachomatous corneal opacity In South Africa, a population-based study (8.2%), and refractive error (4.2%). Blindness and showed that cataract and glaucoma were the major low vision in the extreme Northern Province of causes of blindness in the rural parts of KwaZulu Cameroon has been attributed mainly to cataract9. Natal Province18. A similar study in the Northern A survey10 in South Western Nigeria showed part of South Africa found the prevalence of blind- blindness rate of 0.9%, and cataract, (48.1%) and ness to be 0.5% and women had higher prevalence onchocerciasis (14.8%) were the most common than men19. Cataract (55%), corneal scarring due causes of blindness. Another survey11 in Eastern to trachoma (10%), uncorrected aphakia (9%) and Nigeria also identified cataract (70.6%), glaucoma open angle glaucoma (6%) were found to be major (17.65%) and macular degeneration (5.9%) as causes of blindness19. In 1995, the national popu- the most common (54%) causes of blindness. In lation of South Africa was estimated at about 41 the rural districts of Segou in Mali, cataract was million out of which about 131 000 were estimated reported to be the most common cause of visual to be partially sighted and 262 000 estimated to be loss and was most prevalent among those 50 years blind20. The total number of the visually impaired, of age and older12. Other causes in that study were therefore, was about 400 000. The prevalence of trachoma and glaucoma. In the Central African low vision in South Africa according to these fig- Republic, cataract (51%) was found to be the main ures was reported to be 0.32% and that of blindness cause of blindness, followed by glaucoma (12.7%) was 0.64 per cent20. A more recent study in the and onchocerciasis (8.1%)13. central region of the Limpopo Province of South A survey14 of ocular status of Kenyan rural Africa21, reported prevalence of low vision, mon- communities showed that 0.7% of the population ocular blindness and binocular blindness of 2.43%, sample was blind and another 2.6% were partially 1.77% and 0.73% respectively and the main causes sighted. Cataract, (36% of all blindness) was the of low vision were cataract, corneal opacities major cause of blindness and was responsible for and glaucoma. Other causes were hypertensive 39% of all low vision cases. Other common con- retinopathy, diabetic retinopathy, and trauma. The ditions in that rural Kenya study were non-tracho- main causes of monocular blindness were cataract, The South African Optometrist − June 2005 45 AO Oduntan trauma and infections, while the major causes of 40 years and older in Chile, Brazil and Peru. Age- binocular blindness were cataract, glaucoma, cor- related macular degeneration has been document- neal opacities, and trauma. ed as a leading cause of blindness among elderly Corneal diseases are common in many parts patients in Canada, accounting for 40 to 50% of of Africa and are mainly due to malnutrition or new cases of blindness27. infections such as onchocerciasis and trachoma. Onchocerciasis is a major ocular health problem East Mediterranean and Asia Pacific region in equatorial West Africa. In Liberia22, onchocer- The prevalence of low vision and blindness in ciasis was reported as the cause of all blindness, Asia is relatively high and cataract has been identi- and one-third of low vision. Over half of the visual fied as a major cause. It has been estimated that impairment caused by onchocerciasis was due to the prevalence of blindness in India6 is 1% and posterior segment diseases such as chorioretinal cataract, (80% of blindness cases) has been found disorder and retinal pigment epithelium atrophy. to be a major cause of blindness28, 29. It was further The above review shows that cataract is a estimated that nearly 4 million people are blinded major cause of blindness in all parts of Africa. by cataract in India each year29. In Saudi Arabia, Fortunately, most of the blindness due to cata- the prevalence of low vision and blindness among ract can be reversed following cataract surgery the general population has been reported to be 7.8 with intra-ocular implant or contact or ophthalmic % and 1.5% respectively30 and cataract (52.8%) lenses.