Table of Contents  
REVIEW ARTICLE
Year : 2021  |  Volume : 29  |  Issue : 1  |  Page : 3-12

Diabetic Retinopathy in Sub-Saharan Africa: A Review of Magnitude and Risk Factors


1 Department of Ophthalmology, Federal Medical Centre, Owerri, Imo State, Nigeria
2 Department of Ophthalmology, University of Calabar Teaching Hospital, Cross River State, Nigeria
3 Department of Paediatrics, Federal Medical Centre, Owerri, Imo State, Nigeria

Date of Submission09-Dec-2020
Date of Decision04-Jan-2021
Date of Acceptance21-Mar-2021
Date of Web Publication16-Jul-2021

Correspondence Address:
E. O. Achigbu
Department of Ophthalmology, Federal Medical Centre, Owerri, Imo State
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/njo.njo_49_20

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  Abstract 


Aim: The aim of the study was to provide an updated review on the prevalence and correlates of diabetic retinopathy (DR) in sub-Saharan Africa (SSA). Materials and Methods: A systematic literature search of Medline, Embase, African Journal Online, Africa-Wide Information databases, and Google Scholar for relevant articles was done using a search strategy with key concepts. Studies published between 2010 and 2020 on the prevalence and correlates of DR in SSA were selected. Data on the main study outcomes were extracted into a table based on the study designs. Results: Twenty-seven studies from 12 countries were included. Studies varied in terms of patients’ selection, method of assessing the eye, and retinopathy classification. The reported prevalence range for any DR was 13% to 82.6% and sight-threatening retinopathy 2.1% to 51.4% respectively. Duration of diabetes mellitus and systolic blood pressure were the most common factors associated with an increased risk of DR. Conclusion: There is no recent population-based prevalence of DR in SSA. The available results are however comparable with recent values reported in Europe, America, Middle East, and North Africa. Urgent structured population-based studies on the prevalence of DR are needed for effective public health interventions.

Keywords: Correlates, diabetic retinopathy, prevalence, sub-Saharan Africa


How to cite this article:
Achigbu EO, Agweye CT, Achigbu KI, Mbatuegwu AI. Diabetic Retinopathy in Sub-Saharan Africa: A Review of Magnitude and Risk Factors. Niger J Ophthalmol 2021;29:3-12

How to cite this URL:
Achigbu EO, Agweye CT, Achigbu KI, Mbatuegwu AI. Diabetic Retinopathy in Sub-Saharan Africa: A Review of Magnitude and Risk Factors. Niger J Ophthalmol [serial online] 2021 [cited 2021 Nov 30];29:3-12. Available from: http://www.nigerianjournalofophthalmology.com/text.asp?2021/29/1/3/321649




  Introduction Top


The International Diabetes Federation estimates that 463 million people (9.3%) globally are living with diabetes and this figure is expected to rise to 578 million (10.2%) by 2030 and 700 million (10.9%) by 2045.[1] Diabetes mellitus (DM) is associated with significant mortality, morbidity, and disability.[2] Visual impairment and blindness are end results of ocular complications of diabetes. These complications include cataract and diabetic retinopathy (DR).

DR, a retinal microvascular complication of DM, is the leading cause of preventable blindness in working age adults with a 2.4 times higher risk of blindness than in nondiabetics.[3],[4] DR represents an increasing proportion of all blindness and moderate and severe vision impairment (MSVI) causes worldwide. Age-standardized prevalence of DR-related blindness was noted to be higher in sub-Saharan Africa (SSA) (Central Africa: 0.14%; East Africa, South Africa, and West Africa: 0.21%) South Asia (0.13%), and North Africa/Middle East (0.23%) compared to Asia pacific (0.03%), Asia East (0.03%), Asia Central (0.06%), North America (0.02%), and Europe Central (0.04%).[5] MSVI was also higher in SSA with a range from 0.23% to 0.39%. The highest value was recorded in West Africa and the lowest in South Africa. Asia pacific had a value of 0.09% and North America had 0.08%. This difference was attributed to the intensified prevention and treatment of DR in the high-income countries.[5]

Previous studies focusing on the last decade (1990–2010) reported values in community-based studies in SSA thought to be comparable with American and European population values for any DR and proliferative diabetic retinopathy (PDR).[6] However, most of the studies were hospital based and showed varying prevalence: 7.3% to 62.4% in Southern Africa, 9.5% to 41.1% in East Africa, and 15.0% to 41.1% in West Africa.[6] This study aims to provide an updated review on the prevalence and correlates of DR in SSA. The results of this review may be useful in the development of public health interventions.


  Materials and Methods Top


Search strategy

Two researchers retrieved the papers using Medline, Africa-Wide Information, Embase, African Journal online (AJOL) databases, and Google Scholar search engine. The key concepts searched were: “Prevalence,” “Correlates,” “Diabetic Retinopathy,” and “Sub-Saharan Africa.” Both researchers determined the relevance of each paper to the study question by initially applying the search criteria to the titles and abstracts. Time limits (2010–2020) and language limits (English language) were applied to the search. All studies were limited to humans. All study designs on prevalence and correlates of DR in SSA were included, but studies done outside SSA were excluded from the study.

Data extraction

The papers identified were classified based on the study design (population based or clinic/hospital-based studies). The main findings of the paper, that is, prevalence of DR, prevalence of nonproliferative DR, the prevalence of diabetic macular oedema (DME), prevalence of sight-threatening retinopathy (STR) and correlates (risk factors) were extracted into a table.

Study eligibility

Studies were eligible if they reported on the prevalence of DR and/or risk factors associated with DR. The studies must have been done in SSA and published between 2010 and 2020.

Reliability and quality of studies

The full papers of the retrieved articles were assessed for quality using the Critical Appraisal Skills Programme guidelines for interventional studies[7] and cohort studies[8] and axis appraisal tool for cross-sectional studies.[9] The population-based studies were good quality studies with robust statistical methods, but they were just limited to two countries.

The cohort study used systematic random sampling and compared the findings in a cohort of patients examined in a 2012 study with a pilot done in 2007 to determine the severity of DR. But not all the participants in the previous study were available in the latter study. This may affect the evidence provided by this study. Only two retrospective studies had sample sizes over 1000 and accounted for subjects excluded in their study.

Most of the cross-sectional studies had small sample sizes. Twelve had sample sizes less than 400, five had 100 or less, and only two studies had a sample size of more than 1000. Small sample sizes affect the extrapolation of findings to the general population. In addition, most adopted the consecutive sampling technique and enrolled consenting patients. However, the number of patients invited to participate, the number that declined, and the number of patients served by the clinics were not reported. Self-selection or convenience sampling may introduce a selection bias to the study due to nonrandomization. Only three of the clinic-based studies selected their subjects using a random sampling technique. Four studies calculated sample size and three showed the formula for determining this size. When the method for calculating sample size is not shown, it affects the reproducibility of studies. These methodological errors weaken the evidence of this review. However, it shows the gaps in evidence that needs to be filled in other to determine the prevalence of DR in SSA. Population-based studies are needed to determine the magnitude of DR in SSA.

Compliance with ethical standards

This study did not require ethical clearance or consent from participants as it was a literature review. The authors declare no conflict of interest.


  Results Top


The Medline search yielded 23 abstracts, and 14 were selected that met the selection criteria. Africa-Wide Information yielded 29 abstracts, but only two papers were selected after removal of duplicates and irrelevant papers. Similarly, 46 papers were retrieved from the Embase database, but only five were finally selected. Only one relevant paper was retrieved from AJOL, but it was a duplicate. The Google Scholar search yielded 5025 papers, out of which 43 abstracts were identified after removing irrelevant and duplicate papers. Of these, eight abstracts were retrieved that were relevant to the study. A total of 28 studies were therefore selected for review from 12 countries. One study, a systematic review, was removed as the full paper could not be assessed for appraisal, and so only 27 papers were reviewed.

Study distribution

Eight of the hospital/clinic-based studies originated from Southern Africa, eight from East Africa, seven studies from West Africa, and two from Central Africa. Six of the 11 studies in West Africa were situated in Nigeria and one in Cameroon. East African studies were shared between Ethiopia (four), Kenya (two), Rwanda (one), and Tanzania (one). Central Africa had only two studies and both were carried out in Sudan. The two population-based studies were done in Nigeria and Kenya.

Study designs

Two were population-based studies, one cluster randomized trial and one cohort study, and 23 were hospital/clinic-based cross-sectional studies, including five retrospective reviews. The studies varied based on their patient selection, screening methods, and retinopathy classification methods.

Patient selection

Majority of the studies focused on all diabetic patients. Only three studies worked on type 2 diabetics. There was a lot of variation with the age distribution of the studies. The population-based study in Nigeria worked on patients 40 years and above, while the study in Kenya was among diabetics aged 50 years and above. Two of the hospital/clinic-based studies were on patients 18 years and above, one studied patients 20 years and above, one other study was on patients aged 21 from 90 years, while one had subjects 12 years and above. One study was on children from 10 to 18 years old. Only one study reported on the heterogeneous ethnicity of the patients involved and one specified that study patients were all Africans. Consecutive sampling technique was employed in the sample selection for most (clinic based) of the studies.

Techniques for assessment and classification of diabetic retinopathy

The studies adopted different methods for assessing and classifying DR. Only two studies in Southern Africa used slit lamp biomicroscope (SLB) with indirect noncontact lenses. One study in Central Africa used digital retinal photographs. All except two studies in West Africa used a SLB assessment. The population-based studies and three studies in East Africa used digital retinal photographs. DR was graded using Early Treatment Diabetic Retinopathy Study (ETDRS) or the modified version by some studies. Others used various types of DR grading methods or in some cases, study determined classification. The different methods utilized may affect the grading of DR and limit comparison of findings.

Main Study Outcomes

Hospital/clinic-based studies

There were 25 studies in this category. One had mobile screening centers in addition to a clinic, one was described as a screening center,[5] and one had a clinic with mobile units.[6]

Southern Africa

In Southern Africa, five studies were cross sectional and one a cluster randomized trial,[10],[11],[12],[13],[14] but two were only on type 2 diabetics. Of these two, one reported a prevalence of 32.5% for total prevalence of DR, 4.8% for PDR, and 19.7% for STR,[14] while the second reported a total prevalence of 42% for DR.[15] The other 3 cross sectional studies reported a prevalence of 28. 4%,[10] 52%,[11] and 17.7%[12] [Table 1]. The cohort study in Malawi reported a prevalence of 50.1% for all retinopathy.[16] One retrospective study was limited to type 1 and type 2 diabetics only.[17] Only two studies in Southern Africa reported on prevalence of diabetic maculopathy: 62% in Copperbelt province, Zambia[10] and 20.8% in Tshwane district, South Africa.[13] Duration of diabetes, increasing age, high HbA1C, presence of albuminuria, systolic blood pressure (SBP), and cardiovascular disease were some of the risk factors associated with the development of DR.
Table 1 The studies reviewed and their main outcomes

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West Africa

Five studies from Nigeria, West Africa used a cross sectional research design while one was a retrospective review.[18],[19],[20],[21],[22] and one, a 10-year retrospective review in Lagos state.[23] The studies cut across the north, east, and western parts of the country. However, they had small sample sizes, making it difficult to extrapolate the findings to the general population. The total prevalence of DR reported were: 32.1%,[18] 48.9 %,[19] 15%,[20] 36%,[21] 18.5%.[22] The small sample sizes may also account for the high values reported. The 10-year retrospective review showed a prevalence of 41.6% (n = 84).[23] Three studies reported on the prevalence of PDR as 6.4%,[18] 2%,[20] and 16%.[24] Only one of them reported on diabetic maculopathy as 14.3%.[22] The researchers from Cameroon carried out a cross-sectional study over a 2-year period in the eye clinic involving all diabetics and recorded 40.3% prevalence for all DR, with nonproliferative diabetic retinopathy (NPDR) accounting for 63.4% and PDR 36.6%. Diabetic maculopathy was seen in 14.5%[24] and STR in 18.2% of patients.[24] Duration of diabetes and increasing age were the risk factors associated with the development of DR in multivariate analysis.

Central Africa

There was a paucity of studies from Central Africa. The two studies retrieved were from Sudan.[25],[26] They were both cross-sectional studies, but one was carried out on all diabetics, while the other was on children aged 10 to 18 years. The former recorded a prevalence of 82.6% (n = 316) for all retinopathy, 42.7% for NPDR, and 39.9% for PDR.[25] The latter recorded a prevalence of 33% for all retinopathy and varying prevalence for very mild, mild, and moderate NPDR [Table 1]. There was no report on DME. Duration of DM, SBP, clinically significant macular oedema (CSME), use of oral hypoglycaemics, diabetic foot, amputation, and HbA1c were associated risk factors for DR.

East Africa

There were seven cross-sectional studies identified along with one retrospective review.[27],[28],[29],[30],[31],[32],[33],[34],[35] The prevalence of any retinopathy reported for the cross-sectional studies was 41%,[24] 27.9%,[25] 30.4%,[31] and 41.4%,[32] 31.4%,[33] 31%,[34] and 18.9%.[35] Five studies reported on the prevalence of PDR,[27],[29],[31],[34],[35] and four on the prevalence of diabetic maculopathy (4.7%,[27] 16.1%,[28] 8.7%,[29] and 6%[32]). STR was reported in three studies, one in Kenya (8.3%)[27] and two in Ethiopia (7.3%[32] and 13.7%[33]). Some studies included severe NPDR as part of STR,[33] while another limited it to diabetic maculopathy and PDR.[27] In others, STR was not defined.

Population studies

Two population studies were identified. One was the study on the prevalence and correlates of DR among older people in Nakuru, Kenya (n = 4414).[36] It reported a prevalence of DR of 35.9% following assessment of 277 people with DM.[36] This consisted of 22.1% for NPDR and 13.9% for PDR.[36] Younger age, males, duration of DM, and treatment compliance were risk factors associated[36] with development of retinopathy.

The Nigerian National Blindness and Visual Impairment study of adults 40 years and above reported a prevalence of 20.5% for any retinopathy.[37] PDR had a prevalence of 10.8% and diabetic maculopathy 51.4%. Hypertension and elevated random blood sugar (RBS) were identified correlates of DR.

Mean duration of diabetes and mean age

Seven studies reported on the mean duration of DM. The studies had a mean range of duration of 6 to 8.7 ±7 years.[23],[25],[28],[29],[32] The mean age range of the patients was between 41.20 ± 14.20 and 64 ± 9.34 years [Table 1].[10],[11],[12],[16],[20],[15],[22],[34],[35]


  Discussion Top


This literature review reports on 27 studies from 12 countries in SSA. SSA consists of 54 countries. The paucity of studies, especially population-based studies, may be attributed to the lack of resources as these studies are usually expensive and require the availability of human and material resources, commitment, and time. The reported studies were mostly supported by nongovernmental bodies outside SSA.

The countries not represented may include the francophone speaking countries in West Africa who report their studies in French as English language was applied as a search limit. Other English-speaking countries not represented, especially in Central Africa, may be attributed to lack of resources including human resources to carry out a research.

Methodology of reviewed studies

Most of the studies were cross sectional and clinic based with small sample sizes. The findings should therefore be generalized with caution. Only two studies were population-based cross-sectional studies. One of these was a national blindness and visual impairment survey but reported on the prevalence and correlates of DR[37] (an eligibility criteria). Nation-wide population studies carried out reliably give a true picture of what the true prevalence of DR is and can aid in the planning of health intervention program. Five retrospective reviews were identified. One of the problems of retrospective studies is missing data and incomplete data. These factors were considered by two studies reported here.

Prevalence of diabetic retinopathy and maculopathy

One of the population-based studies reported a prevalence of 35.9% for all retinopathy, 22% of these had NPDR and13.9% PDR.[36] Approximately 33% of all subjects in this study had DME.[36] In the second study,[37] 20.5% of the subjects had DR. NPDR was found in 72.9% of these and PDR in 10.8%.[37] More than half (51.4%) of the subjects had DME.[37] These studies were also reported in a previous review in Africa (Jan 1999–2011).[6] In the decade under review (2010–2020), no population-based study on the prevalence of DR was carried out in SSA. Egypt in North Africa reported a prevalence of 20.5% for any DR similar to the population-based study in Nigeria; however, they had a lower value of 2.3% for PDR.[6] A lower value for PDR (3.4%) was also reported in Tunisia compared with the SSA countries.[38] The reported prevalence of DR in Tunisia was 26.3%.[38]

In the Middle East region, the prevalence of DR ranges from 19% in the United Arab Emirate to 64% in Jordan.[39] The former is similar to the prevalence in Nigeria, while Iraq with a DR prevalence of 37% is similar to the prevalence reported in the Kenya population-based study.[39] In Europe, Germany and Austria reported no DR prevalence of 79.88% with 10.26% of mild to moderate NPDR and 9.09% of severe NPDR and PDR. Diabetic maculopathy was 0.77%.[40] This shows a prevalence of any DR comparable to our finding in SSA (Nigeria) but a wide difference in diabetic maculopathy values. Similar findings were noted in New Zealand[41] with a DR prevalence of 22.5% and Denmark with a no DR prevalence of 78%, 18% for NPDR, and 4% for PDR.[42]

The Singapore Epidemiology of Eye Diseases Study from 2004 to 2011 reported high values of any retinopathy (33.9%) similar to Kenya and 26.3% for STR.[43] In a pooled analysis of eight population-based studies to determine the prevalence of DR among diabetics in the United States of America (USA), the estimated overall crude prevalence of DR among persons with DM was 40.3% (95% confidence interval [CI] [95% CI], 38.8–41.7%) and the estimated overall crude prevalence of vision threatening diabetic retinopathy was 8.2% (95% CI, 7.4–9.1%).[44] The overall prevalence is higher than 35.9% and 20.5% recorded in the two population-based studies in SSA.[36],[37] However, with the exclusion of the Wisconsin Epidemiologic Study of Diabetic Retinopathy (WESDR)[45] results (conducted between 1980 and 1982), the prevalence drops to 35.8% and 7.3%, respectively, for all retinopathy and STR similar to the SSA (Kenya) findings. A more recent survey in the USA reported a crude prevalence of 28.5% (95% CI, 24.9–32.5%) for DR and 4.4% (95% CI, 3.5–5.7%) for STR among persons with diabetes aged 40 years and above.[46] This is lower than the values in the previous meta-analysis. The authors opined that the reduction noted in the prevalence of DR may be related to improved diabetes care as there are reports of reduced hospitalization for amputation and end-stage renal disease.

It is important to note that most of the studies cited in this review were done after the SSA population-based studies and so the similarities noted in the prevalence of DR may not apply if new surveys are undertaken in SSA. The value may be higher in SSA going by some of the results of the clinic-based studies.

The clinic-based studies reported varying prevalence for DR. In Southern Africa, the study in Blantyre, Malawi reported a lower prevalence (32.5%)[14] compared with the cohort study[16] also done later in Malawi. In fact, the cohort study showed a higher prevalence of any retinopathy (50.1%), STR (7.3%), and proliferative retinopathy(29.4%)[16] than was reported in the 2007 pilot study (any retinopathy 32.0%, STR 19.6%, proliferative retinopathy 5.7%).[14] The latter, however, did not demonstrate any progressive increase in DR prevalence or incidence in a cohort of diabetics over the 5 years unlike the WESDR that showed a 4-year progression of DR and progression to PDR in 41.2% and 10.5% of subjects with type 1 DM. Insulin treated patients with type 2 DM and non-insulin treated patients also had a 4 year progression in 34% and 24.9% subjects respectively.[45] A recent study in Kwazulu-Natal, South Africa reported a higher prevalence (42%) than the 20.5% reported in a previous study in Johannesburg[17] in the previous decade. This difference may also be attributed to the wide disparity in sample size. The former[15] studied 385 type 2 diabetics and the latter[17] over 3000 type 2 diabetics.

In the West African subregion, the prevalence of any DR appeared to have increased from 15% in 2008[20] to 36% in 2009[21] and dropped to 32% in 2015[18] with a further decrease in 2016 to 18.5%[22] for all diabetics. While this may appear as some positive progress in the management of diabetes and its complications, the findings may be due to the differences in the methodologies, different sample population as the studies were carried out in different regions of the country, and the effect of small sample sizes. Small sample sizes increase the margin of error and reduce the power of studies.

In Ethiopia, the prevalence of any DR increased from 13.0% in 2015[28] to 18.9% in 2019[34] and 31.4% in 2020[33] for roughly similar sample sizes but different regions of the country. Owing to the small sample sizes of clinic-based studies, the findings should be interpreted and extrapolated with caution to the community. In a study to report the estimated prevalence of DR from 30 United Kingdom National Health Service (NHS) hospital trusts (April 2000–Nov 2010), 76.2% had DR with 65.6% NPDR and 10.6% had PDR.[46] These figures are higher than those in SSA population-based studies, but the authors reported the difficulty in extrapolating their data to the entire United Kingdom (UK) population as there are few reliable data on the prevalence of DM in the NHS.[47] It is important to note that these subjects were already registered and being managed in a health intervention scheme.Many of these studies graded retinopathy using a SLB with indirect noncontact lenses and this has been found to underestimate DR compared with digital retinal photography.[36] Stereoscopic retinal photograph is the method of choice for assessing and grading DR.

Risk factors for diabetic retinopathy

The risk factors associated with the development of DR noted in this review spans many themes. However, the duration of diabetes, SBP, age at onset, and increasing age were the most notable from multivariate regression analysis. These findings have been corroborated by other studies.[45],[48],[49] Others include the level of glycated haemoglobin (HbA1c), RBS, albuminuria (reflecting renal disease), diabetic foot, and amputation.

Implications for policy and practice

To reduce the burden of DR in SSA, screening and treatment programs need to be established at different levels of health care. This will require collaboration of all the critical stakeholders for advocacy toward favorable policies and political commitment. One critical tool to achieving this is data on the prevalence of DR. Scientific evidence has been described as a potent tool to garner political will for screening programs.[50] The evidence in this review is weakened by the methodological issues of the studies identified. Prior to the development of a national screening programme in Botswana, an epidemiological survey identified DR as the second leading cause of blindness after cataract. Based on this evidence, stakeholders including the Ministry of Health, Diabetes Association of Botswana, Medical School of Botswana amongst others converged and designed a national screening programme for the country.[50] Similarly, in the UK,[51] diabetologists, ophthalmologists, public health doctors and optometrists worked together before the commencement of the national screening programme in 2003. They provided an evidence base for STR before the development of the program and considered key issues, including the politics of funding, availability of assessment and treatment facilities, the cohort to screen, and how to reach them among others.[50] These set the template for their program. A similar strategy can be adapted by SSA at national, regional, and hospital levels.


  Conclusion Top


Varying prevalence was identified in this review from 12 countries in SSA. The prevalence from the population-based studies was comparable with that reported from other countries in Europe, Middle East, North Africa, and USA, but the SSA studies were conducted before 2010, earlier than the other studies. In addition, most regions in SSA are yet to document population prevalence of DR. The hospital-based studies showed different regional trends in the prevalence of DR based on studies done before and after 2010, but the small sample sizes make it difficult to extrapolate the findings to the general population. The lack of data and methodological issues noted weaken the evidence in this review. Well-structured population-based studies are needed for strong evidence on the prevalence of DR in SSA before effective public health interventions can be developed.

Recommendations

Population-based studies are needed to determine the national and regional prevalence of DR in SSA. This will enable proper planning of interventions. Interdisciplinary collaborations between relevant stakeholders are needed to achieve this as well as effective interventions.

National and state diabetic registers, screening centers, training of personnel, awareness, and education of all involved including patients on the need to be registered and screened are strongly recommended as the odds of developing DR is higher among those with poor control compared to those with good glycemic control.[34]

Limitations

The full papers of some studies were not found. These papers were excluded from the study, thus limiting the number of studies assessed in this review. Some studies, though published after 2010, were done before 2010, and so their findings may not reflect the current picture prevalent in these countries. In addition, limiting the review to only articles written in English may have excluded relevant studies.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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