Abstract and Introduction
Abstract
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.
Introduction
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. In contrast about 12–19%, of persons with type 2 diabetes have some DR already at the time of diagnosis, with 4% developing proliferative DR after 20 years or more of diabetes. 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.
The St Vincent Declaration (1989) recommended that new onset blindness arising from DR should be reduced by a third within 5 years. 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. 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, in persons aged 12 years and older. The recommendation of screening beginning from the age of 12 years reflects the low incidence of DR, and especially proliferative DR, in younger children. 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).
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. The prevalence of diabetes in Wales is currently estimated at approximately 5%, with 160 000 people affected. Following a pilot regional programme, 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.
The prevalence of DR has previously been described for several populations, using different methods for the detection and classification of DR which accounts in part for the broad variations observed. A recent systematic review, 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.