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Table of Contents
ORIGINAL ARTICLE
Year : 2021  |  Volume : 3  |  Issue : 1  |  Page : 17

Prevalence and risk factors for diabetic retinopathy in Nigeria: A systematic review and meta-analysis


1 Department of Medicine, Endocrinology Unit, University College Hospital, Ibadan, Nigeria
2 Department of Ophthalmology, University College Hospital, Ibadan, Nigeria

Date of Submission15-Feb-2021
Date of Acceptance08-Apr-2021
Date of Web Publication18-May-2021

Correspondence Address:
Dr. Taoreed Adegoke Azeez
Department of Medicine, Endocrinology Unit, University College Hospital, Ibadan
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/pajo.pajo_82_21

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  Abstract 


Introduction: The prevalence of diabetes mellitus and its complications is rising globally. Diabetic retinopathy is one of the most common microvascular complications of diabetes and is the most common cause of blindness in adults globally. The aims of this study were to determine the pooled prevalence of diabetic retinopathy in Nigeria and to identify the associated risk factors.
Methods: Medical databases including PubMed, Google Scholar, African Journals online, Cochrane library, EMBASE, and SCOPUS were searched for studies on diabetic retinopathy in Nigeria between the years 2000 and 2020 using the MESH terms “diabetic retinopathy,” “prevalence,” “risk factors,”, “Nigeria.” The gray literature was also searched. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were strictly adhered to in selecting the studies. The outcome variables of interest were prevalence of diabetic retinopathy in Nigeria as well as risk factors associated with diabetic retinopathy. The Newcastle-Ottawa scale was used to assess the quality and bias of the selected studies. Statistical analyses were performed using Stata version 14.3. DerSimonian and Laird random-effect model was used. Heterogeneity was assessed using the I2 statistic.
Results: Twenty studies met the eligibility criteria and they were selected for the studies. The total sample size was 3299. I2 statistic was 99%, which suggests a high level of heterogeneity among the selected studies. Using the random-effect model, the pooled prevalence of diabetic retinopathy in Nigeria was 21.3% (95% confidence interval 21.1–21.5). The most common risk factors for diabetic retinopathy in Nigeria were duration of diabetes, poor glycemic control, and hypertension.
Conclusion: The prevalence of diabetic retinopathy in Nigeria is high and there is a need to improve the glycemic control of patients with diabetes so as to prevent or delay its onset.

Keywords: Diabetic retinopathy, meta-analysis, Nigeria, prevalence, risk factors, systematic review


How to cite this article:
Azeez TA, Adediran OA, Eguzozie EC, Ekhaiyeme E. Prevalence and risk factors for diabetic retinopathy in Nigeria: A systematic review and meta-analysis. Pan Am J Ophthalmol 2021;3:17

How to cite this URL:
Azeez TA, Adediran OA, Eguzozie EC, Ekhaiyeme E. Prevalence and risk factors for diabetic retinopathy in Nigeria: A systematic review and meta-analysis. Pan Am J Ophthalmol [serial online] 2021 [cited 2021 Jun 22];3:17. Available from: https://www.thepajo.org/text.asp?2021/3/1/17/316304




  Introduction Top


Diabetes mellitus refers to a heterogeneous group of metabolic disorders characterized by chronic hyperglycemia which is due to a defect in insulin secretion, action or a variable combination of both.[1] As of 2020, the global prevalence of diabetes mellitus was 422 million, according to the World Health Organization (WHO) statistics.[2] In Sub-Saharan Africa, Nigeria has the largest number of people living with diabetes mellitus with an estimated prevalence of 5.77%.[3],[4] Ekolu et al. have reported that chronic complications of diabetes are common in Sub-Saharan Africa and eye diseases are prominent among these complications.[5]

Diabetic retinopathy is one of the most prominent microvascular complications of diabetes mellitus.[6] Diabetic retinopathy is the commonest ocular complication of diabetes.[7] [Table 1] shows the proportion of diabetic retinopathy among the ocular manifestations of diabetes as reported from various studies.[8],[9],[10],[11],[12],[13],[14],[15]
Table 1: Proportion of diabetic retinopathy among ocular complications of diabetes mellitus

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Diabetic retinopathy typically progresses through 2 stages namely: nonproliferative diabetic retinopathy (NPDR) and proliferative diabetic retinopathy (PDR). NPDR features the earliest retinal changes detectable on dilated fundoscopy such as microaneurysms, dot and blot intraretinal hemorrhages, hard exudates as well as intraretinal microvascular anomaly.[6] NPDR is further subdivided into mild, moderate, and severe stages.[15] In the absence of optimal glycemic control, NPDR invariably progresses to PDR characterized by retina neovascularization. Neovascularization may occur on or within one disc diameter of the optic disc (NVD), elsewhere in the posterior pole of the fundus (NVE) or both. Retinal detachment is a sight threatening complication of proliferative retinopathy. The most common cause of loss of vision in patients with diabetic retinopathy is diabetic macula edema.[15],[16]

Landmark trials such as the Diabetes Control and Complications Trial and the United Kingdom Prospective Diabetes Study have demonstrated a strong correlation between hyperglycemia and the development of diabetic retinopathy.[16],[17] Some of the proposed pathophysiological pathways underlying diabetic retinopathy include accelerated formation of advanced glycated end-products, polyol pathway flux, activation of protein kinase C pathway, and reductive-oxidative stress.[17] Other important mechanisms that have been reported in the literature include increased expression of growth factors such as vascular endothelial growth factor (VEGF) and insulin-like growth factor-1, subclinical inflammation, activation of the renin-angiotensin-aldosterone system , and deleterious microvascular hemodynamic changes.[17] The pathophysiologic pathways are summarized in [Figure 1].
Figure 1: The pathophysiological pathways of diabetic retinopathy

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Diabetic retinopathy is the leading cause of blindness in adults (between 20 and 70 years) in the developed world.[18] In a landmark blindness and visual impairment survey done in Nigeria, cataract was the most common cause of blindness while diabetic retinopathy was the 5th most common cause.[19] Pandova, however, remarked that diabetic retinopathy is rapidly becoming a prominent cause of blindness even in the developing countries.[20] In the early stages, diabetic retinopathy does not usually impair vision, but the late stages may present with varying degree of visual impairment or blindness.[18] Therefore, early detection is key to preventing or delaying the late changes. Screening for diabetic retinopathy is often done by indirect dilated ophthalmoscopy, in conjunction with a handheld superfield lens, a binocular indirect ophthalmoscope or by fundus photography using a conventional film or digital camera. However, Onakpoya et al. reported that screening for diabetic retinopathy has a high default rate.[21]

In a cross-sectional study, involving over 13 000 patients with type 2 diabetes, Liu and his co-researchers in China reported duration of diabetes, poor glycemic control, hypertension, and dyslipidemia as risk factors for diabetic retinopathy.[22] A case-control study in Brazil involving 240 individuals also reported similar findings in addition to diabetic nephropathy as risk factors for diabetic retinopathy.[23] Therefore, good glycemic control is central to the prevention and delay of progression of diabetic retinopathy.[18] Intravitreal anti-VEGF central to the treatment of PDR. Laser photocoagulation is useful in selected cases. Vitrectomy is indicated in cases of persistent vitreous hemorrhage and/or tractional retinal detachment.

There are a few studies on diabetic retinopathy conducted in Nigeria. Furthermore, these studies have reported a wide range of prevalence of diabetic retinopathy. The sample sizes in the studies were also small making it difficult to draw conclusions.

Objectives

  1. To determine the pooled prevalence of diabetic retinopathy in Nigeria
  2. To identify the risk factors for diabetic retinopathy among Nigerian patients living with diabetes mellitus.



  Methods Top


Retrieval of studies and selection processes

Medical databases including PubMed, Google Scholar, African Journals online, Cochrane library, EMBASE, and SCOPUS were searched for studies on diabetic retinopathy in Nigeria between January 1, 2000 and December 31, 2020. The pre-print server medRxiv was also searched. Using the Medical Subject Headings (MeSH), the terms “diabetic retinopathy,” “prevalence,” “risk factors,” “Nigeria” and a combination of the terms were searched. Boolean operators such as “AND” as well as “OR” were also used. The grey literature was also searched to improve the depth of the studies retrieved. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were strictly adhered to in selecting the studies. The PRISMA flow diagram is shown in [Figure 2].
Figure 2: The PRISMA flow diagram

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Inclusion criterion

Studies done on the prevalence with or without risk factors for diabetic retinopathy in Nigeria.

Exclusion criteria

  1. Studies on the prevalence of diabetic retinopathy done outside Nigeria.


Studies on diabetic retinopathy done within Nigeria but not focused on the prevalence and risk factors for diabetic retinopathy.

Data extraction and analysis

Abstracts and full texts were appraised independently by the authors. Disagreements were resolved by consensus. The outcome variables of interest were prevalence of diabetic retinopathy in Nigeria as well as risk factors associated with diabetic neuropathy. Diabetic retinopathy was diagnosed by direct ophthalmoscopy and/or by using a slit lamp and either a contact lens or a 78D lens and/or by using a fundal camera. Confidence interval (CI) was computed for each study and the pooled prevalence was determined. Data extracted were initially obtained on a spreadsheet before it was transferred to a statistical tool. The Newcastle-Ottawa scale was used to assess the quality and bias of the selected studies. Statistical analyses were done using Stata version 14.3 (StataCorp LLC, TX, USA). DerSimonian and Laird random-effect model was used. Heterogeneity was assessed using the I2 statistic.


  Results Top


Twenty studies met the eligibility criteria and were selected for the analysis. [Table 2] shows the distribution of the studies in terms of the geopolitical zones in Nigeria. There is no statistically significant correlation between the number of studies and prevalence of diabetes across the geopolitical zones (P = 0.691; r = −0.209).
Table 2: Number of selected studies and prevalence of diabetes across the geopolitical zones in Nigeria

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[Table 3] shows the selected studies, sample size and prevalence of diabetic retinopathy in Nigeria. The total sample size was 3299. I2 statistic was 99% which suggests a high level of heterogeneity among the selected studies. Using the random-effect model, the pooled prevalence of diabetic retinopathy in Nigeria was 21.3% (95% CI 21.1%–21.5%). [Figure 3] shows the forest plot of the meta-analysis.
Table 3: Prevalence of diabetes in Nigeria

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Figure 3: Forest plot

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[Table 4] shows the risk factor for diabetic retinopathy in Nigeria. [Figure 4] depicts the frequency by which the risk factors were reported from various studies. The most common risk factors for diabetic retinopathy in Nigeria were duration of diabetes, poor glycemic control, and hypertension.
Table 4: Risk factor for diabetic retinopathy in Nigeria

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Figure 4: Frequency of reportage of the risk factors

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  Discussion Top


The studies that met the eligibility criteria for the meta-analysis were limited. Lee et al. have also reported that the epidemiologic studies on diabetic retinopathy are limited.[44] Screening for diabetic retinopathy is not frequently practiced and this may contribute to the limited amount of epidemiologic studies on retinopathy.[45] The inadequate number of Ophthalmologists in Nigeria might have also contributed to the limited number of available studies on diabetic retinopathy in Nigeria.[46]

The pooled prevalence rate of diabetic retinopathy in Nigeria, as observed in this meta-analysis is 21.3% (95% CI 21.1%–21.5%). In a meta-analysis of Chinese studies on diabetic retinopathy, Song et al. reported a pooled prevalence rate of 18.5%, which is similar to the findings of the present study.[47] Similarly, in Tanzania (another developing nation in sub-Saharan Africa like Nigeria), Cleland et al., reported the prevalence rate of diabetic retinopathy as 27.9%.[48] In addition, a Zimbabwean study also reported a prevalence rate of 28.4% which is in keeping with what was found in this meta-analysis.[49] A major reason why the prevalence of diabetic retinopathy is high in Nigeria could be because a large number of Nigerian patients with diabetes have sub-optimal glycemic control which is a major risk factor for diabetic retinopathy.[50]

The most commonly reported risk factors for diabetic retinopathy, as found in this systematic review, were poor glycemic control and prolonged duration of diabetes. Several authors, in other parts of the world, have also reported similar findings in their studies.[23],[51],[52],[53] This is in keeping with the reports of previous authors who had documented that optimal glycemic control can prevent or delay the onset of diabetic retinopathy.[54],[55] Chronic hyperglycemia, in a patient with prolonged duration of diabetes mellitus, increases the period of exposure of the retinal cells to the metabolic processes mediating retinal microangiopathy and capillary non-perfusion, thereby increasing the risk of developing diabetic retinopathy.[56]

This study shows that hypertension and diabetes are significant risk factors associated with the development of diabetic retinopathy. Chang et al. also reported a significant association between diabetic retinopathy and dyslipidemia.[57] Atchison et al. observed that hypertension is associated with development of diabetic retinopathy.[52] Other risk factors for diabetic retinopathy identified in this study included obesity, the age of the patient, smoking, and diabetic nephropathy. Lee et al. have also documented that diabetic nephropathy and smoking were significantly associated with the development of diabetic retinopathy in their study.[58] Furthermore, some researchers, working in Germany have linked obesity with the development of diabetic neuropathy.[59]

The main strength of this meta-analysis is the generation of a pooled national prevalence of diabetic retinopathy, which will serve as an indicator for tracking disease prevalence in Nigeria and measuring impact of control efforts.


  Conclusion Top


The prevalence of diabetic retinopathy in Nigeria is high. The identified risk factors are sub-optimal glycemic control, long duration of diabetes, hypertension and the age of the patient. Others are smoking, dyslipidemia, obesity, age of onset of diabetes, and diabetic nephropathy. It is therefore recommended that a closer attention should be paid to glycemic control and comorbidities such as hypertension, diabetes, and obesity in patients with diabetes to alleviate the burden of diabetic retinopathy.

Limitations

There is significant heterogeneity in the sociodemographics and methods of recruiting the patients. Furthermore, there was limited number of studies that met the eligibility criteria.

Consent for publication

The authors hereby give the journal the consent to publish the article.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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