Blindness Survey Methods: Response from Sudan Study Authors
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Funding: The authors received no specific funding for this article.
Competing Interests: The authors have declared that no competing interests exist.
Citation: Ngondi J, Ole-Sempele F, Onsarigo A, Matende I, Baba S, et al. (2007) Blindness Survey Methods: Response from Sudan Study Authors. PLoS Med 4(2): e86 doi:10.1371/journal.pmed.0040086
Jeremiah Ngondi (jn250@cam.ac.uk)
Carol Brayne, University of Cambridge, Cambridge, United Kingdom
Francis Ole-Sempele, Christian Mission Aid, Nairobi, Kenya
Alice Onsarigo
Ibrahim Matende, The Carter Center, Nairobi, Kenya
Samson Baba, South Sudan Ministry of Health, Juba, South Sudan
Fiona Matthews, Medical Research Council Biostatistics Unit, Cambridge, United Kingdom
Paul M. Emerson, The Carter Center, Atlanta, Georgia, United States of America
We thank the authors [1,2] for the two perspectives on our articles [3,4]. Our study estimated the prevalence of blindness in Mankien at 4%, which Kuper and Gilbert describe as being “beyond the range” of the studies reviewed by Pascolini et al. [5]. The review did not include any studies from the ten states that compose southern Sudan. The nearest surveys reported were conducted in 1998 in Al-Ginena province of Southern Darfur—which is within the 16 northern states of Sudan governed from Khartoum, and was not directly affected by the war in the south. The Al-Ginena studies show a blindness prevalence of 3.2% in all ages [6,7]. Yet despite the geographical proximity, two decades of civil war in the south were accompanied by the absence of a health infrastructure, and no preventive health services to speak of, which makes southern Sudan unique. Comparisons with other parts of Sudan or with other countries are probably not justified or meaningful.
Our survey was conducted in Mankien, which was anecdotally known to be endemic for severe blinding trachoma, and this was subsequently confirmed by our trachoma survey, which showed an overall prevalence of trichiasis and bilateral corneal opacity of 9.6% and 3.1%, respectively [3]. The prevalence of blinding cataract in Mankien was consistent with expectation, and would presumably have been higher had there been a systematic over-sampling of the blind. It is the prevalence of blinding trachoma that sets the population apart from all others reported and reviewed by Pascolini et al. These survey data from Mankien are extremely valuable in that they demonstrate the way uncontrolled trachoma can ravage inaccessible and underserved communities who have, quite literally, been off the map until recently. The war affected the whole of southern Sudan, and extremely high levels of active trachoma and trichiasis have been observed in all the areas that we have managed to survey in recent years [8]. Although not generalizable to the ten southern states, these data from Mankien are probably indicative of the overall situation in southern Sudan.
We acknowledge the survey limitations highlighted by Kuper and Gilbert, and have addressed them in the discussion. Our sampling methodology has been used in similar surveys in Kenya [9], Bangladesh [10], Tehran [11], Cameroon [12], and Pakistan [13]. Use of basic eye examination technique by auxiliary health-care workers in blindness surveys has been suggested for settings without ophthalmologists [14], which is entirely consistent with what the integrated eye care workers are trained to do. Kuper and Gilbert's difficulty appears to stem from the findings, rather than the methodology. They offer two interpretations to explain the data, whilst not acknowledging the most parsimonious explanation, and that is that these data are an accurate reflection of the situation on the ground; we cannot risk not accepting this. The international community must rise to the challenge of planning and offering service for blindness prevention interventions in these desperately needy communities. We should not let an academic argument as to whether the prevalence of blindness is really 4% or whether it is, perhaps, a little lower be the basis for continued neglect.
We fully agree with both Kuper and Gilbert, and Buchan that there is need for a concerted effort to survey the entire region, provide resources, and deliver services to the marginalized and poverty stricken communities in southern Sudan.
References
Kuper H, Gilbert C (2006) Blindness in Sudan: Is it time to scrutinise survey methods PLoS Med 3: e476–doi:10.1371/journal.pmed.0030476 doi:10.1371/journal.pmed.0030476.
Buchan J (2006) Visual loss in postconflict southern Sudan. PLoS Med 3: e450–doi:10.1371/journal.pmed.0030450 doi:10.1371/journal.pmed.0030450.
Ngondi J, Ole-Sempele F, Onsarigo A, Matende I, Baba S, et al. (2006) Blinding trachoma in postconflict southern Sudan. PLoS Med 3: e478–doi:10.1371/journal.pmed.0030478 doi:10.1371/journal.pmed.0030478.
Ngondi J, Ole-Sempele F, Onsarigo A, Matende I, Baba S, et al. (2006) Prevalence and causes of blindness and low vision in southern Sudan. PLoS Med 3: e477–doi:10.1371/journal.pmed.0030477 doi:10.1371/journal.pmed.0030477.
Pascolini D, Mariotti SP, Pokharel GP, Pararajasegaram R, Etya'ale D, et al. (2004) 2002 global update of available data on visual impairment: A compilation of population-based prevalence studies. Ophthalmic Epidemiol 11: 67–115.
Mohamedain MA (2000) Prevalence survey of trachoma and its complications in Al-Ginena province. Khartoum (Sudan): University of Khartoum.
Abusin S (2002) Prevalence and causes of blindness in the Sudan: A review of published and unpublished data Khartoum (Sudan): University of Khartoum.
Ngondi J, Onsarigo A, Adamu L, Matende I, Reacher M, et al. (2005) The epidemiology of trachoma in Eastern Equatoria and Upper Nile States, southern Sudan. Bull World Health Organ 83: 904–912.
Whitfield R, Schwab L, Ross-Degnan D, Steinkuller P, Swartwood J (1990) Blindness and eye disease in Kenya: Ocular status survey results from the Kenya Rural Blindness Prevention Project. Br J Ophthalmol 74: 333–340.
Dineen BP, Bourne RR, Ali SM, Huq DM, Johnson GJ (2003) Prevalence and causes of blindness and visual impairment in Bangladeshi adults: Results of the National Blindness and Low Vision Survey of Bangladesh. Br J Ophthalmol 87: 820–828.
Fotouhi A, Hashemi H, Mohammad K, Jalali KH (2004) The prevalence and causes of visual impairment in Tehran: The Tehran Eye Study. Br J Ophthalmol 88: 740–745.
Oye JE, Kuper H, Dineen B, Befidi-Mengue R, Foster A (2006) Prevalence and causes of blindness and visual impairment in Muyuka: A rural health district in South West Province, Cameroon. Br J Ophthalmol 90: 538–542.
Jadoon MZ, Dineen B, Bourne RR, Shah SP, Khan MA, et al. (2006) Prevalence of blindness and visual impairment in Pakistan: The Pakistan National Blindness and Visual Impairment Survey. Invest Ophthalmol Vis Sci 47: 4749–4755.
Thylefors B (1987) A simplified methodology for the assessment of blindness and its main causes. World Health Stat Q 40: 129–141.(Jeremiah Ngondi, Francis Ole-Sempele, Al)
Competing Interests: The authors have declared that no competing interests exist.
Citation: Ngondi J, Ole-Sempele F, Onsarigo A, Matende I, Baba S, et al. (2007) Blindness Survey Methods: Response from Sudan Study Authors. PLoS Med 4(2): e86 doi:10.1371/journal.pmed.0040086
Jeremiah Ngondi (jn250@cam.ac.uk)
Carol Brayne, University of Cambridge, Cambridge, United Kingdom
Francis Ole-Sempele, Christian Mission Aid, Nairobi, Kenya
Alice Onsarigo
Ibrahim Matende, The Carter Center, Nairobi, Kenya
Samson Baba, South Sudan Ministry of Health, Juba, South Sudan
Fiona Matthews, Medical Research Council Biostatistics Unit, Cambridge, United Kingdom
Paul M. Emerson, The Carter Center, Atlanta, Georgia, United States of America
We thank the authors [1,2] for the two perspectives on our articles [3,4]. Our study estimated the prevalence of blindness in Mankien at 4%, which Kuper and Gilbert describe as being “beyond the range” of the studies reviewed by Pascolini et al. [5]. The review did not include any studies from the ten states that compose southern Sudan. The nearest surveys reported were conducted in 1998 in Al-Ginena province of Southern Darfur—which is within the 16 northern states of Sudan governed from Khartoum, and was not directly affected by the war in the south. The Al-Ginena studies show a blindness prevalence of 3.2% in all ages [6,7]. Yet despite the geographical proximity, two decades of civil war in the south were accompanied by the absence of a health infrastructure, and no preventive health services to speak of, which makes southern Sudan unique. Comparisons with other parts of Sudan or with other countries are probably not justified or meaningful.
Our survey was conducted in Mankien, which was anecdotally known to be endemic for severe blinding trachoma, and this was subsequently confirmed by our trachoma survey, which showed an overall prevalence of trichiasis and bilateral corneal opacity of 9.6% and 3.1%, respectively [3]. The prevalence of blinding cataract in Mankien was consistent with expectation, and would presumably have been higher had there been a systematic over-sampling of the blind. It is the prevalence of blinding trachoma that sets the population apart from all others reported and reviewed by Pascolini et al. These survey data from Mankien are extremely valuable in that they demonstrate the way uncontrolled trachoma can ravage inaccessible and underserved communities who have, quite literally, been off the map until recently. The war affected the whole of southern Sudan, and extremely high levels of active trachoma and trichiasis have been observed in all the areas that we have managed to survey in recent years [8]. Although not generalizable to the ten southern states, these data from Mankien are probably indicative of the overall situation in southern Sudan.
We acknowledge the survey limitations highlighted by Kuper and Gilbert, and have addressed them in the discussion. Our sampling methodology has been used in similar surveys in Kenya [9], Bangladesh [10], Tehran [11], Cameroon [12], and Pakistan [13]. Use of basic eye examination technique by auxiliary health-care workers in blindness surveys has been suggested for settings without ophthalmologists [14], which is entirely consistent with what the integrated eye care workers are trained to do. Kuper and Gilbert's difficulty appears to stem from the findings, rather than the methodology. They offer two interpretations to explain the data, whilst not acknowledging the most parsimonious explanation, and that is that these data are an accurate reflection of the situation on the ground; we cannot risk not accepting this. The international community must rise to the challenge of planning and offering service for blindness prevention interventions in these desperately needy communities. We should not let an academic argument as to whether the prevalence of blindness is really 4% or whether it is, perhaps, a little lower be the basis for continued neglect.
We fully agree with both Kuper and Gilbert, and Buchan that there is need for a concerted effort to survey the entire region, provide resources, and deliver services to the marginalized and poverty stricken communities in southern Sudan.
References
Kuper H, Gilbert C (2006) Blindness in Sudan: Is it time to scrutinise survey methods PLoS Med 3: e476–doi:10.1371/journal.pmed.0030476 doi:10.1371/journal.pmed.0030476.
Buchan J (2006) Visual loss in postconflict southern Sudan. PLoS Med 3: e450–doi:10.1371/journal.pmed.0030450 doi:10.1371/journal.pmed.0030450.
Ngondi J, Ole-Sempele F, Onsarigo A, Matende I, Baba S, et al. (2006) Blinding trachoma in postconflict southern Sudan. PLoS Med 3: e478–doi:10.1371/journal.pmed.0030478 doi:10.1371/journal.pmed.0030478.
Ngondi J, Ole-Sempele F, Onsarigo A, Matende I, Baba S, et al. (2006) Prevalence and causes of blindness and low vision in southern Sudan. PLoS Med 3: e477–doi:10.1371/journal.pmed.0030477 doi:10.1371/journal.pmed.0030477.
Pascolini D, Mariotti SP, Pokharel GP, Pararajasegaram R, Etya'ale D, et al. (2004) 2002 global update of available data on visual impairment: A compilation of population-based prevalence studies. Ophthalmic Epidemiol 11: 67–115.
Mohamedain MA (2000) Prevalence survey of trachoma and its complications in Al-Ginena province. Khartoum (Sudan): University of Khartoum.
Abusin S (2002) Prevalence and causes of blindness in the Sudan: A review of published and unpublished data Khartoum (Sudan): University of Khartoum.
Ngondi J, Onsarigo A, Adamu L, Matende I, Reacher M, et al. (2005) The epidemiology of trachoma in Eastern Equatoria and Upper Nile States, southern Sudan. Bull World Health Organ 83: 904–912.
Whitfield R, Schwab L, Ross-Degnan D, Steinkuller P, Swartwood J (1990) Blindness and eye disease in Kenya: Ocular status survey results from the Kenya Rural Blindness Prevention Project. Br J Ophthalmol 74: 333–340.
Dineen BP, Bourne RR, Ali SM, Huq DM, Johnson GJ (2003) Prevalence and causes of blindness and visual impairment in Bangladeshi adults: Results of the National Blindness and Low Vision Survey of Bangladesh. Br J Ophthalmol 87: 820–828.
Fotouhi A, Hashemi H, Mohammad K, Jalali KH (2004) The prevalence and causes of visual impairment in Tehran: The Tehran Eye Study. Br J Ophthalmol 88: 740–745.
Oye JE, Kuper H, Dineen B, Befidi-Mengue R, Foster A (2006) Prevalence and causes of blindness and visual impairment in Muyuka: A rural health district in South West Province, Cameroon. Br J Ophthalmol 90: 538–542.
Jadoon MZ, Dineen B, Bourne RR, Shah SP, Khan MA, et al. (2006) Prevalence of blindness and visual impairment in Pakistan: The Pakistan National Blindness and Visual Impairment Survey. Invest Ophthalmol Vis Sci 47: 4749–4755.
Thylefors B (1987) A simplified methodology for the assessment of blindness and its main causes. World Health Stat Q 40: 129–141.(Jeremiah Ngondi, Francis Ole-Sempele, Al)