Aims Determine the prevalence and severity of diabetic retinopathy (DR) and risk factors in a large community based screening programme, in order to accurately estimate the future burden of this specific and debilitating complication of diabetes.
Methods A cross-sectional analysis of 91 393 persons with diabetes, 5003 type 1 diabetes and 86 390 type 2 diabetes, at their first screening by the community based National Diabetic Retinopathy Screening Service for Wales from 2005 to 2009. Image capture used 2×45° digital images per eye following mydriasis, classified by qualified retinal graders with final grading based on the worst eye.
Results The prevalence of any DR and sight-threatening DR in those with type 1 diabetes was 56.0% and 11.2%, respectively, and in type 2 diabetes was 30.3% and 2.9%, respectively. The presence of DR, non-sight-threatening and sight-threatening, was strongly associated with increasing duration of diabetes for either type 1 or type 2 diabetes and also associated with insulin therapy in those with type 2 diabetes.
Conclusions Prevalence of DR within the largest reported community-based, quality assured, DR screening programme, was higher in persons with type 1 diabetes; however, the major burden is represented by type 2 diabetes which is 94% of the screened population.
- Public health
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Diabetic retinopathy (DR) continues to be an important microvascular complication in type 1 and type 2 diabetes. Previous evidence suggests that DR is evident in approximately 50% of persons with type 1 diabetes for 28 years and advanced DR after 39 years.1 In contrast about 12–19%,2 ,3 of persons with type 2 diabetes have some DR already at the time of diagnosis,4 with 4% developing proliferative DR after 20 years or more of diabetes.2 In the UK and USA, DR unfortunately remains among the leading causes of blindness and low vision, along with age related macular degeneration and glaucoma.5–8
The St Vincent Declaration (1989) recommended that new onset blindness arising from DR should be reduced by a third within 5 years.9 However, it is only in the last decade that significant progress has been made in implementing screening programmes to detect and monitor DR. To date many different DR screening models have been introduced worldwide.10–19 In the UK the National Screening Committee for England and Wales (1999) produced guidelines for DR screening programmes to ensure standardisation and quality assurance. The recommended screening procedure includes assessment of visual acuity and obtaining digital fundal photographs following mydriasis,20 in persons aged 12 years and older.21 The recommendation of screening beginning from the age of 12 years reflects the low incidence of DR, and especially proliferative DR, in younger children.22 In Scotland a three tiered screening approach has been implemented which involves obtaining only one macular centred digital fundal photograph per eye without mydriasis (tier 1) and if unsuccessful then mydriasis is used (tier 2) and finally biomicroscopy with a slit lamp if photography remains unsuccessful (tier 3).23
Wales currently has a population of 3.06 million which is predominantly Caucasian, with the majority situated in the industrial south (∼60%) with the remainder of the country generally regarded as rural.24 The prevalence of diabetes in Wales is currently estimated at approximately 5%, with 160 000 people affected.25 Following a pilot regional programme,26 a national DR screening programme, the Diabetic Retinopathy Screening Service for Wales (DRSSW) was commissioned in 2002. The aim of the service was initially to identify all undiagnosed sight-threatening DR and facilitate timely onwards referral to hospital eye services (HES). The secondary aim was to identify the presence of any DR so that improvements in glycaemic control, hypertension and dyslipidaemia could be implemented where necessary.20
The prevalence of DR has previously been described for several populations,8 ,27 using different methods for the detection and classification of DR which accounts in part for the broad variations observed. A recent systematic review,27 conducted an individual participant analysis to estimate the global prevalence of DR and also to determine the major risk factors by pooling a total 35 studies (22 896 people) conducted between 1980 and 2008 in the USA, Australia, Europe and Asia. The studies obtained retinal photographs using a mixture of 35 mm film and digital images, through dilated and undilated pupils capturing between one and nine fields per eye with a minority photographing one eye only. There were also several different grading protocols used to ascertain the prevalence and severity of DR.
The objective of our study was to accurately determine the prevalence of DR at entry into a national screening programme using standardised protocols and quality-assured methodology for photography and grading and also to explore the relationship between certain putative risk factors with the presence of any lesions of DR and also the presence of sight-threatening DR in persons with type 1 and type 2 diabetes.
Materials and methods
DRSSW is a community-based mobile screening service. Habitual Visual acuity (VA) is recorded (with or without glasses or with pinhole) using a 3 m illuminated Snellen chart and two 45° fields (one macula centred and one nasal) digital fundal photographs are captured following mydriasis (1% tropicamide) followed by grading by accredited retinal graders. Images are stored on laptop computers and then downloaded daily onto a central server, either directly or via a secure internet connection. DRSSW employs 30 photographic teams consisting of a healthcare professional and an accredited photographer who conduct the screening at 220 locations throughout Wales. The Canon DGi digital camera is used to acquire the digital images which are centrally graded using a standardised grading protocol (table 1). All the key elements are subject to quality control procedures. At the time of screening all persons are asked to sign a two part consent form. The first part is to give consent for mydriasis to be instilled and for retinal photographs to be taken. The second part is for consent for their anonymised data and images to be used for teaching and research purposes. Only the data for those individuals who provided both consents were included in this study.
Persons with diabetes aged 12 years or above who are registered with a general practitioner (GP) in Wales and not already under the care of HES for DR related reasons, are required to be referred to DRSSW accompanied by demographic and diagnostic information. These referrals from GP's form the single collated list of persons for screening. On a monthly basis the lists are compiled and sent to each GP practice for validation. Of those known to have diabetes in Wales 8.4% were ineligible for screening as 6.5% were already under the care of HES for DR related reasons, 1.6% were excluded due to medical reasons and 0.4% were under the age of 12 years (19.3% of those who were eligible for screening did not attend appointments). All persons invited for screening are sent an appointment letter with a date, time and venue for screening. All letters have a reminder that all appointments and venues can be changed to a time and place more suitable for the individual. DRSSW currently (2013) has an uptake rate of 80% for screening. Those who do not attend screening appointments are sent additional appointments within 3 months and their GPs are informed of their non-attendance and are asked to remind their patients of the importance of attending screening.
DRSSW uses a grading protocol which evolved from the European handbook for screening9 and all subsequent changes were made by consensus with ophthalmologists across Wales as part of the All Wales Ophthalmology group who provide advice and guidance to DRSSW on DR and referrals to HES. Subjects with DR were subdivided into two groups: non-sight-threatening DR (NSTDR) which included those with background DR and preproliferative DR (PPDR); and sight-threatening DR (STDR), that is, maculopathy and/or proliferative DR (table 1). As retinal thickening or clinically significant macular oedema is not discernible on non-stereoscopic images, maculopathy was defined as definite exudates or haemorrhages (with an unexplained VA of worse than 6/12) within one disc diameter of the fovea. Both eyes were assessed for DR and the worse grade from the two eyes used in the analysis. All persons with unassessable images in one or both eyes that had not previously been seen by an ophthalmologist were referred to HES for assessment. Where only one eye was assessable the presence or absence of DR relied on this eye as was the grading of DR if present. The National Screening Committee definition of unassessable images is used by DRSSW.30
Characteristics of the study population were described using means (SD) for continuous variables with percentages for categorical variables. For comparisons, T tests and χ2 tests were used, respectively, with a p value of <0.05 used to indicate statistical significance. Logistic regression analyses were performed to assess the association of the routinely collected variables with retinopathy status, separately for each type of diabetes. The continuous variables of age at diagnosis of diabetes and duration of diabetes were categorised to avoid assuming linearity, with different categories used for type 1 and type 2 diabetes to ensure equal distribution among the groups. For type 1 diabetes, age at diagnosis was divided into subgroups ≤12 yrs, 13–23 yrs and ≥24 yrs and diabetes duration into subgroups <10 yrs, 10–19 yrs and ≥20 years. For type 2 diabetes the subgroups for age at diagnosis were ≤55 yrs, 56–66 yrs and ≥67 yrs and for diabetes duration were <5 years, 5–9 years and ≥10 years, respectively. OR and 95% CI for each were calculated.
From January 2005 to November 2009, 91 393 persons with type 1 or type 2 diabetes were screened by DRSSW. The demographic characteristics of the participants are included in table 2. The overall prevalence of any DR within this population was 32.4% (95% CI 32.1% to 32.7%), NSTDR 29.0% (95% CI 28.7% to 29.3%) and STDR 3.4% (95% CI 3.3% to 3.5%). The prevalence of any DR was 56.3% in persons with type 1 diabetes and 30.9% in persons with type 2 diabetes. NSTDR prevalence was 45.1% in type 1 diabetes and 28.1% in type 2 diabetes. For STDR the prevalence in type 1 diabetes was 11.2% and in type 2 diabetes was 2.9%. The prevalence of the different categories of DR are shown in table 2.
The characteristics of subjects with and without DR at initial screening are compared in table 3, with the former group divided into NSTDR and STDR. In subjects with type 1 diabetes, those with STDR were more likely to be male, younger at the time of diagnosis, with a longer duration of diabetes and therefore older at first screening compared with those without DR. Participants with type 2 diabetes and STDR were also more likely to be male, younger at the screening event and with a longer duration of diabetes, and in addition were more likely to be receiving insulin therapy compared with those without DR.
The results of the logistic regression analysis are shown in table 4. For subjects with type 1 diabetes the OR for each type of DR was significantly higher in those aged 12–23 years at diagnosis and significantly lower in those aged over 23 years when compared with those aged below 12 years at diagnosis. Men also had increased odds of all severities of DR compared with women. The OR of all severity grades of DR increased sharply with duration of diabetes. There was a 7.90-fold and 20.60-fold increased odds of any DR associated with a duration of diabetes of 10–19 years and ≥20 years compared with <10 years and a 28.22-fold and 85.84-fold increased odds of STDR in the same subgroups, respectively. For type 2 diabetes the ORs of any DR and NSTDR were significantly higher (1.18 and 1.24, respectively) in those aged over 66 years at diagnosis of diabetes than in subjects aged 55 years or less at diagnosis. However the OR of STDR decreased (0.60 and 0.58) with increasing age at diagnosis of diabetes. Men had increased odds of all grades of DR compared with women. The odds of all grades of DR increased with increasing duration of diabetes. For any DR the odds increased by a factor of 1.60 with a known duration of diabetes of 5–9 years and almost 3.71-fold for a known duration of diabetes of 10 years or more compared with less than 5 years and for STDR the odds increased from 1.83-fold to 6.76-fold in the same subgroups, respectively. The use of insulin had ORs of 2.77 for any DR and 7.24 for STDR compared with those using diet alone.
This study provides estimates of the baseline prevalence of DR for subjects over the age of 12 years and not receiving care at the HES for DR related reasons, when attending for the first time at DRSSW. In the population studied the prevalence of any DR, NSTDR and STDR in subjects with type 1 diabetes were 56.3%, 45.0% and 11.2%, respectively, and in type 2 diabetes were 30.9%, 27.7% and 2.9%, respectively. The presence of NSTDR and STDR was strongly associated with increasing duration of diabetes with either type 1 or type 2 diabetes and was also associated with insulin therapy in those with type 2 diabetes.
The strength of this study is the large population size that underwent systematic screening using standardised quality assured procedures and equipment for photography and grading. Graders and photographers were accredited. The exclusion of subjects who did not participate in screening is a limitation. The exclusion of those persons with diabetes under the care of HES because of DR is likely to lead to an underestimation, however currently the extent of this difference is not known. Although PPDR is the level at which referral to HES is required by screening programmes in the UK, it was excluded from the category of STDR in this study so that it was more comparable with the category of STDR reported in previous studies. Also the limited availability of putative risk factors which included only duration and treatment of diabetes with glycaemic control, blood pressure and lipid status not collected by the DRSSW is a limitation and will be addressed in future studies.
The comparison of the prevalence rates for DR between studies is inherently difficult due to the changing classification of diabetes over time and the different grading protocols employed, as well as differences in population characteristics.8 ,27 ,31–34 Web appendix 1 shows the prevalence rates found in previous studies worldwide. In other UK screening programmes the prevalence of any DR has been reported at 53.5% for type 1diabetes,33 and 19.2–25.3% for type 2 diabetes,3 ,32 ,33 which were lower than that seen in our study population at 56.0% and 30.3%, respectively. Also in comparison, in Iceland the prevalence of DR was slightly lower in type 1 diabetes and higher in type 2 diabetes at 51.7%34 and 41.0%,31 respectively. A recent meta-analysis found a much higher prevalence of DR in type 1 diabetes at 77.3%27 and a slightly lower prevalence in type 2 diabetes at 25.2%.27 Retinal image capture (number of images and the use or not of mydriasis) may contribute to some of these differences as well as duration of diabetes. Our study clearly demonstrates that increased duration of diabetes is associated with a higher prevalence of DR. The prevalence of STDR previously reported in the UK has been 16.4% in type 1 diabetes and 1.9% and 6.0% in type 2 diabetes.3 ,32 ,33 In our study the prevalence of STDR was a little lower in persons with type 1 diabetes at 11.2%. Differences in the classification of STDR such as the inclusion or exclusion of PPDR and definitions of maculopathy may explain the differences.32 ,33 We had essentially similar prevalence of STDR at 2.9% in type 2 diabetes. The Scottish screening programme reported the prevalence in 47 090 newly diagnosed type 2 diabetes and this short duration is likely to be the reason for the low prevalence of DR reported at 19.3% for any DR and 1.9% for RDR.3
Increasing duration of diabetes was the most significant risk factor for the presence of any DR, NSTDR and STDR in subjects with type 1 and type 2 diabetes. The ORs were much higher in type 1 diabetes compared with type 2 diabetes, however the duration of diabetes was also longer with subgroups of <10 years, 10–19 years and ≥20 years compared with <5 years, 5–9 years and ≥10 years, respectively. The risk of all grades of DR increased with duration of diabetes being particularly high in those with diabetes duration of 20 years or more for type 1 diabetes and 10 years or more for type 2 diabetes.
In our study we observed an increased risk of all severities of DR associated with the use of insulin after adjusting for all other confounders. For type 2 diabetes this may reflect a more advanced disease state and we interpret this as likely to be an epiphenomenon and not a direct result of insulin therapy. Glycaemia and duration of diabetes have previously been shown to be highly associated with the presence of DR along with elevated blood pressure and cholesterol levels.4 ,8 ,33 ,35–38
To date this study represents the largest reported community-based national DR screening programme for detecting the presence of DR, especially STDR. The findings will provide our policy makers with important information for planning eye care services, with the proviso that the prevalence of STDR may be underestimated because of those already within HES. The strong association with disease duration demonstrates the importance of early detection and referral to a screening programme. The detection of STDR at an early stage is essential to ensure timely onward referral for further assessment and possible treatment to improved outcome. Detection of NSTDR provides the physician with an opportunity to improve, where necessary, glycaemic and blood pressure control to prevent the progression of DR. A structured screening programme is expected to reduce blindness by 40% within 4 years.29 Addressing issues of non-attendance currently at approximately 20% will contribute greatly to the success of such programmes to ensure optimal cost benefit of any DR screening service, especially poignant in times of austerity.
The authors acknowledge the staff at the DRSSW for their support and especially Gavin Bhakta the data manager at the DRSSW and Digital Healthcare for providing the anonymised database used in this study.
This web only file has been produced by the BMJ Publishing Group from an electronic file supplied by the author(s) and has not been edited for content.
Files in this Data Supplement:
- Data supplement 1 - Online supplement
Contributors All authors contributed to the writing of this report. RLT processed, analysed and interpreted the data. FDD provided statistical advice and analysis. DRO, SDL and RLG contributed to the conception, study design, interpretation of the data. SRC contributed to processing and interpreting the data and SLH and RVN provided expert advice. All authors revised and approved the final version of this manuscript. DRO had full access to all of the data in this study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Funding St David's Medical Foundation and Takeda provided unrestrictive educational grants.
Competing interests None.
Ethics approval All data from those persons who consented at screening for their anonymous data to be used in research was anonymised at source by the data manager prior to being provided to the study team for analysis. R&D and ethics approval was sought for this study; however both panels decided the study was a service evaluation and not research and as such R&D and ethical approval was not required.
Provenance and peer review Not commissioned; externally peer reviewed.