|Year : 2013 | Volume
| Issue : 1 | Page : 17-22
Prevalence and causes of blindness: Results from the rapid assessment of avoidable blindness survey in gezira state, sudan
Kamal Hashim Binnawi1, Awad Hassan Mohamed1, Balgis Alkhair Alshafae1, Zainab Abdalla2, Mazin Alsanosi2, Mamoun Mirghani Ahmed3, Fadwa Hashim Binnawi3
1 National Program for Prevention of Blindness, Khartoum, Alneelain University, Khartoum, Sudan
2 The Carter Center, Khartoum, Sudan
3 Alsayem Eye Hospital, Gezira University, Madani, Sudan
|Date of Web Publication||21-Sep-2013|
Kamal Hashim Binnawi
Alneelain University, Khartoum
Objectives: To estimate the prevalence of avoidable blindness in people aged 50 years and older in Gezira state, Sudan, using the Rapid Assessment for Avoidable Blindness methodology. Design: Cross-sectional, population-based survey. Participants: Forty-three clusters of 50 people aged 50 years or older were selected by probability proportionate to size sampling of clusters. Households within clusters were selected through compact segment sampling. A total of 2150 eligible persons were selected, of whom 2103 (97.8%) persons were examined. Materials and Methods: Participants underwent a comprehensive ophthalmic examination in their homes by specially trained ophthalmic teams, including measurement of visual acuity (VA) with a tumbling-E chart and the diagnosis of the principal cause of visual impairment. Results: The prevalence of bilateral blindness (presenting VA <3/60) was 9.37% (95% confidence interval [CI] ±1.95) and the prevalence of bilateral visual impairment (VA of <6/18-6/60) was 3.9% (95% CI ±1.10) in the sample. Definite avoidable causes of blindness (i.e., cataract, refractive error, trachoma and corneal scarring) were responsible for 74.6% of bilateral blindness. Cataract was the major cause of blindness (57.4%), followed by glaucoma (17.3%). Conclusions: The prevalence of blindness in people aged 50 years and older in Gezira state was slightly higher than that expected. Than main cause of blindness was cataract, followed by glaucoma. Three quarters of blindness was due to avoidable causes.
Keywords: RAAB, blindness, Sudan, vision 2020
|How to cite this article:|
Binnawi KH, Mohamed AH, Alshafae BA, Abdalla Z, Alsanosi M, Ahmed MM, Binnawi FH. Prevalence and causes of blindness: Results from the rapid assessment of avoidable blindness survey in gezira state, sudan. Sudanese J Ophthalmol 2013;5:17-22
|How to cite this URL:|
Binnawi KH, Mohamed AH, Alshafae BA, Abdalla Z, Alsanosi M, Ahmed MM, Binnawi FH. Prevalence and causes of blindness: Results from the rapid assessment of avoidable blindness survey in gezira state, sudan. Sudanese J Ophthalmol [serial online] 2013 [cited 2019 May 21];5:17-22. Available from: http://www.sjopthal.net/text.asp?2013/5/1/17/118641
| Introduction|| |
The World Health Organization (WHO) estimates that there are 45 million people in the world who are blind (vision worse than 3/60 in the better eye with presenting vision). , This is expected to rise to 76 million by 2020 if the current services are not improved. Vision 2020 is a joint initiative by the WHO and the International Association for the Prevention of Blindness that aims to eliminate avoidable blindness by the year 2020. ,,, The priority diseases in the first phase of Vision 2020 are cataract, refractive error and low vision, childhood blindness, onchocerciasis and trachoma. These conditions constitute more than 75% of blinding diseases  and are amenable to effective preventive and curative interventions.
The first step in achieving this target is to obtain baseline data on visual impairment at country and sub-country (state, district) levels for planning and monitoring eye care programs.
The WHO estimates for the East Mediterranean Region (EMR), which includes Sudan, suggest that the prevalence of blindness is 7% in the population aged 50 years and above.  Population-based data in relation to prevalence of blindness in Sudan are rather deficient. The national program for prevention of blindness estimates that 1.5% of the population is blind. The main causes of blindness, according to the NPPB estimates, are cataract, trachoma, glaucoma and other diseases including onchocerciasis, responsible for 60%, 18%, 17% and 5%, respectively.  Sudan adopted Vision 2020 in 2003. Since then, the cataract surgical rate (CSR), which is the number of cataract surgeries per million population per year, increased from 560 to 2025 cataract surgeries per year per million population. The SAFE strategy for trachoma is applied in 12 out of 15 northern states of Sudan. The number of ophthalmologists increased from 60 in 2003 to 260 in 2009. There is remarkable variation in the CSR between different states. In 2009, the reported CSR was 1696 in Gezira state compared with a CSR exceeding 7000 in Khartoum (the capital city). Likewise, there is marked discrepancy in access to other components of eye care between the center and the peripheries. 
Large-scale surveys of blindness are expensive and time consuming. The Rapid Assessment of Avoidable Blindness (RAAB) is a rapid survey method. It is rapid because it measures visual impairment only in those aged over 50 years, who account for over 80% of the blindness in the population yet a small proportion of the total population size. RAAB includes detailed data on causes of low vision and blindness besides cataract, and has an updated data entry and analysis package. Many countries in Africa conducted RAAB surveys to generate baseline data for planning Vision 2020 activities. ,,,
The objective of this study is to estimate the prevalence and causes of blindness in Gezira state using the RAAB survey methodology.
| Materials and Methods|| |
When deciding on the sample size, it was assumed that the population size of adults aged 50 years and older in Gezira state is 310,208, the prevalence of blindness in people aged 50 years and older is 7%,  the required confidence is 95%, the precision is 20%, the design effect is1.5 and the non-response rate is10%.
Population data were generated from the Sudan national census in 2008, where the percentage of population aged 50 years and older was 9.6%. 
The required sample size in Gezira state was 2150 individuals. The fieldwork was carried out in December 2010. The clusters were selected with probability-proportionate to size using updated data from the 2008 national census as the sampling frame. Households within clusters were selected through compact segment sampling. Maps of the enumeration area showing major landmarks and the approximate distribution of households were obtained or drawn. Enumeration areas were then divided into 43 segments, each including approximately 50 people aged 50 years and older. The first house in the segment was selected at random by drawing lots. The survey team then visited that house and neighboring houses in that segment, door to door, until 50 people aged 50 years and older were identified. If the target number of 50 people was not reached, another segment was chosen at random and sampling continued. If an eligible household member was absent, at least two return visits were made. Information about visual status was ascertained from relatives or neighbors for people who were not available after repeated visits.
Visual acuity (VA) was measured with a tumbling-E chart with a Snellenoptotype size 6/18 on one side and size 6/60 on the other side at a distance of 6 m. Pinhole vision was measured if the VA was less than 6/18 in either eye. All measurements were taken in full daylight with available correction and people were categorized according to presenting visual acuity (PVA) with available correction as follows:
- Blind: PVA 3/60 in the better eye
- Severely visually impaired: PVA <6/60 to 3/60 in the better eye
- Visually impaired: PVA <6/18 to 6/60 in the better eye
- Normal vision: PVA 6/18 or better in the better eye.
The lens status of all individuals was assessed by specially trained ophthalmic residents and ophthalmic medical assistants using a torch and direct ophthalmoscope in a shaded or dark environment without dilatation of the pupil. All people with presenting VA <6/18 were examined by an ophthalmologist using a direct ophthalmoscope or portable slit lamp, as appropriate. The principal cause of blindness or visual impairment was recorded, assigning the major cause to the primary disorder or (if there are two existing primary disorders that contribute equally to the visual impairment) the cause registered was that which is easiest to treat.
All survey teams received structured training. The inter-observer agreement for measurement of VA, lens examination and cause of blindness was assessed between the teams to ensure that it was of an acceptable standard (ie, kappa >0.60).
Special software (RAAB program version 4.02) was used for data entry and automatic standardized data analysis. The prevalence estimates took account of the design effect (DEFF) when estimating the confidence intervals.
Ethical approval for this work was granted by the Sudanese Federal Ministry of Health. All participants gave verbal consent for the examination. All people with operable cataract or other treatable conditions were referred for free treatment.
| Results|| |
The study population consisted of 2150 individuals. Twenty-five (1.2%) individuals were not available, seven (0.3%) individuals refused to be examined and 15 (0.7%) individuals were not capable to be examined; therefore, 2103 (97.8%) individuals were included in the survey. The mean age of those who individuals were examined was 62.9 years, while it was 65.3, 70.1 and 70.0 years for those who were unavailable, those who refused and those who were not capable, respectively.
The examined sample included 1098 men (52.2%) and 1005 women (47.8%). [Table 1] shows the age and sex composition of the population aged 50 years and above in Gezira state and [Table 2] shows the age and sex composition of the population in the same age groups in the examined sample. There was a slight overrepresentation of people aged 65 years old and above, with a corresponding slight underrepresentation in the younger age groups in the sample.
There were 197 bilaterally blind people, giving a sample prevalence of blindness of 9.37% (95% CI, ±1.95) [Table 3]. The prevalence of severe visual impairment was 3.9% (95% CI, ±1.1) and the prevalence of visual impairment was 10.79% (95% CI, ±1.92). The age- and gender-adjusted prevalence of blindness was 7.68% (95% ±1.95), that of severe visual impairment was 3.36% (95% CI, ±1.1) and that of visual impairment was 9.71% (95% CI, ±1.92) [Table 4].
|Table 1: Age and sex composition of the population (50 years and above) in Gezira state|
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|Table 2: Age and sex composition of the population (50 years and above) in the examined sample|
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|Table 3: Prevalence of blindness, severe visual impairment (CVI) and visual impairment (VI) in the sample (age and sex not adjusted)|
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|Table 4: Age- and sex-adjusted prevalence of blindness, severe visual impairment (CVI) and visual impairment (VI) in people aged 50 years and above in Gezira state|
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Extrapolating the survey data to the age and gender distribution of Gezira state, in people aged 50 years and older, there were an estimated 13,251 blind men and 10,580 blind women, 5670 severely visually impaired men and 4740 severely visually impaired women and 18,356 visually impaired men and 11,770 visually impaired women [Table 5].
|Table 5: Estimated cases of blinding diseases (in people aged 50 years and above) in Gezira state|
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Assuming that 80% of blindness is in people aged over 50 years, the population-prevalence of blindness can be estimated to be 0.8%.
Untreated cataract was the primary cause of bilateral blindness (53.8%) [Table 6]. Posterior segment disease (including glaucoma, diabetic retinopathy and age-related macular degeneration [AMD]) accounted for 25.4% of bilateral blindness. Glaucoma was the second cause, responsible for 17.8% of bilateral blindness. Corneal scarring and trachoma complications were third, responsible for 11.1%. Surgical complications, uncorrected aphakia and diabetic retinopathy accounted for 5.1%, 3.0% and 1.5% of bilateral blindness, respectively. Refractive errors caused only 0.5% of bilateral blindness. Avoidable causes - that is, cataract (including unoperated and postoperative complications), refractive error, trachoma and other causes of corneal scars - were responsible for 74.6% of bilateral blindness.
|Table 6: Principal causes of blindness in persons: VA <3/60 in the better eye with available correction|
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| Discussion|| |
Prevalence of Visual Loss
The age- and gender-adjusted prevalence of blindness (VA <3/60 with available correction) in Gezira state is 7.68% (95% CI, ±1.95), that of severe visual impairment is 3.36% (95% CI, ±1.1) and that of visual impairment is 9.71% (95% CI, ±1.92) in people aged 50 years and older. These were similar in men and women. The prevalence of blindness was assessed only in those aged 50 years or older; however, the prevalence is low in those aged under 50 years. The prevalence of blindness in Gezira state is slightly higher than that expected by the WHO for Sudan. Estimates of blindness for the WHO-EMR region suggest that 7% people aged 50 years and older are blind.  The prevalence estimate in Gezira state is higher than that in most of the African countries where RAAB surveys were conducted. ,, Other RAAB surveys in other states of Sudan showed the prevalence of blindness to be 4.90% in Northern state, 7.38% in Sinnar, 8.77% in North Kordofan and 14.% in Kassala.  Extrapolating these results for the total population of Gezira state, the prevalence of blindness in all ages is estimated to be 0.7%. This is far lower than the previous national estimate in 2003 of 1.5% prevalence of blindness in Sudan.  That reduction in the prevalence of blindness may be attributed to an increase in cataract surgical services in Gezira state in the previous years.
Causes of Visual Loss
Cataract was the major cause of blindness (53.8%). This is similar to the other reported studies from Sudan  and the current global estimate.  Altogether, nearly 75% of all blindness was attributed to definitely avoidable causes - again, similar to the global estimates. This does not include cases of glaucoma and diabetic retinopathy, which are potentially avoidable and classed as diseases of the posterior segment. The RAAB survey was designed to be rapid and field based to diagnose avoidable causes of blindness; therefore, the ability to diagnose posterior segment causes of blindness accurately was low. The diagnosis of refractive error depended on the accuracy of measurement of VA, and did not allow differentiation between types of refractive errors.
| Acknowledgments|| |
The authors would like to express their gratitude to all those who made this work possible. Sight Savers are thanked for their generous grant that covered all the cost of this work. The Carter Center assistance in data management and transportation saved the authors a lot of time and resources. Ophthalmic residents and medical assistants did wonderful field work. Mr. Elfatih M. Osman, managing director of the National Program for Prevention of Blindness, and his staff endeavored in tackling administrative issues. The Gezira state ministry of health was very supportive and, last but not least, the community cooperation and generosity that exceeded all the authors' expectations.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]