Use of personalised risk-based screening schedules to optimise workload and sojourn time in screening programmes for diabetic retinopathy: A retrospective cohort study

Background National guidelines in most countries set screening intervals for diabetic retinopathy (DR) that are insufficiently informed by contemporary incidence rates. This has unspecified implications for interval disease risks (IDs) of referable DR, disparities in ID between groups or individuals, time spent in referable state before screening (sojourn time), and workload. We explored the effect of various screening schedules on these outcomes and developed an open-access interactive policy tool informed by contemporary DR incidence rates. Methods and findings Scottish Diabetic Retinopathy Screening Programme data from 1 January 2007 to 31 December 2016 were linked to diabetes registry data. This yielded 128,606 screening examinations in people with type 1 diabetes (T1D) and 1,384,360 examinations in people with type 2 diabetes (T2D). Among those with T1D, 47% of those without and 44% of those with referable DR were female, mean diabetes duration was 21 and 23 years, respectively, and mean age was 26 and 24 years, respectively. Among those with T2D, 44% of those without and 42% of those with referable DR were female, mean diabetes duration was 9 and 14 years, respectively, and mean age was 58 and 52 years, respectively. Individual probability of developing referable DR was estimated using a generalised linear model and was used to calculate the intervals needed to achieve various IDs across prior grade strata, or at the individual level, and the resultant workload and sojourn time. The current policy in Scotland-screening people with no or mild disease annually and moderate disease every 6 months-yielded large differences in ID by prior grade (13.2%, 3.6%, and 0.6% annually for moderate, mild, and no prior DR strata, respectively, in T1D) and diabetes type (2.4% in T1D and 0.6% in T2D overall). Maintaining these overall risks but equalising risk across prior grade strata would require extremely short intervals in those with moderate DR (1-2 months) and very long intervals in those with no prior DR (35-47 months), with little change in workload or average sojourn time. Changing to intervals of 12, 9, and 3 months in T1D and to 24, 9, and 3 months in T2D for no, mild, and moderate DR strata, respectively, would substantially reduce disparity in ID across strata and between diabetes types whilst reducing workload by 26% and increasing sojourn time by 2.3 months. Including clinical risk factor data gave a small but significant increment in prediction of referable DR beyond grade (increase in C-statistic of 0.013 in T1D and 0.016 in T2D, both p < 0.001). However, using this model to derive personalised intervals did not have substantial workload or sojourn time benefits over stratum-specific intervals. The main limitation is that the results are pertinent only to countries that share broadly similar rates of retinal disease and risk factor distributions to Scotland. Conclusions Changing current policies could reduce disparities in ID and achieve substantial reductions in workload within the range of IDs likely to be deemed acceptable. Our tool should facilitate more rational policy setting for screening. Author summaryWhy was this study done? People with diabetes are advised to have their eyes photographed regularly to detect early retinal changes so that they can be referred for preventive treatments for diabetic retinopathy. In some countries, including Scotland, national health service programmes of regular screening have been set up. Deciding how often such screening should occur is a complex problem that depends on the individual risk of developing disease but also on system-level issues such as how much screening workload can be delivered, what level of disease progression between screens is deemed acceptable (interval disease risk), whether the system should be designed to ensure this risk is equal for all (equity), and the acceptable time for someone to be in a progressed state before detection (sojourn time). Our aim was to use contemporary data from the Scottish screening programme accrued over 10 years to enable policy makers and individuals to make better informed decisions about how often screening should occur and the design of screening programmes. Previous studies were much smaller, used data from earlier decades, when disease rates were higher, or only examined type 1 diabetes (T1D) or type 2 diabetes (T2D), not both. What did the researchers do and find? We took data on retinal photograph screenings from 128,606 screening examinations in people with T1D and 1,384,360 screenings in people with T2D with associated clinical risk factor data collected between 2007 and 2016. We quantified the current rates of disease occurrence and built a predictive model to allow those at more risk to be differentiated from those at lower risk. We used the current rate data and the risk model to quantify what the workload, sojourn time, and equity effects would be of different screening interval policies. We created an online tool to enable policy makers to evaluate the effects of different choices about screening intervals. The current system used in Scotland and elsewhere achieves low overall risks, but with large differences in risks between individuals. The prediction modelling showed that using lots of clinical risk factor data refines the prediction of progression of disease only slightly beyond using just diabetes type and the information contained in the last retinal photograph. What do these findings mean? We show how much the current system could reduce differences in risk by screening some people more often and others less often, and show that can be achieved at the same time as substantially reducing workload. The main limitation is that the results are pertinent only to countries that share broadly similar rates of retinal disease and risk factor distributions to Scotland, where the study was done.