Measuring Outcomes of Diabetic Retinopathy Screening: What Is Important?

Screening for diabetic retinopathy (DR) is now well established in clinical practice, and in some systems it is considered a measure of adherence to best practice. The article by Silva et al. in this issue of Diabetes Care (1) investigates self-awareness of DR and whether planned follow-up is concordant with national guideline recommendations.

Screening developed after laser photocoagulation intervention was shown to be successful in preventing vision loss when initiated during the asymptomatic but late stages of DR (2,3). Iceland introduced nationwide screening in 1980, and investigators found a subsequent reduction in blindness from DR compared with other geographically co-located countries (4,5). Subsequently, for other countries, investigators found a reduction in vision loss after introduction of screening (6,7) compared with historical control participants. In parallel, there have been substantial improvements in diabetes care that slow DR development and progression (8).

A screening program alone will not reduce vision loss. There needs to be appropriate timely referral for ophthalmological interventions, which, in addition to traditional laser therapy, now include intravitreal pharmacotherapy such as anti-VEGF and steroid injections. Guidelines for screening and, critically, intervals for repeat screening have been established. As mild DR progresses through stages to vision-threatening diabetic retinopathy (vtDR), intervals between screenings are shortened according to documented severity (9).

Crucially, people with diabetes need to understand the reasons for screening and be able to attend screening and timely ophthalmological interventions to prevent blindness (Fig. 1). Silva et al. (1) are to be applauded on their investigation of whether people with diabetes are aware of their retinopathy status and its required follow-up. Collection of these data occurred during routine endocrinology visits during which the people with diabetes underwent eye examinations and answered interview questions. The study was carried out over a 10-year period at the Joslin Diabetes Center, a tertiary-care diabetes-specific academic medical center. A particular strength of the study is that a large number (25,360) of people with diabetes participated. The cohort is well characterized, with a mean age of 53.4 years and diabetes duration of 13.4 years; mean HbA_1c was 8%, and 62% had type 2 diabetes.

The authors found significant disparities between self-awareness and retinal imaging findings. The participants represented 30% of all people with diabetes accessing diabetes care at the Joslin Diabetes Center, but they were not accessing eye care at Joslin. There was high uptake of the questionnaire and gradable retinal images (94.3%). Despite concurrent finding of vtDR, 55% reported no DR and, correspondingly, 49% reported follow-up discordant with guideline recommendations.

The major conclusion for health care professionals (HCP) is that many people with diabetes are not able to accurately report their DR status despite reporting attendance for recent screening. This was despite reporting that their last eye exam was within 2 years (86%), within 12 months (62%), within 6 months (40%), and within 3 months (23%). The weakness of the study is the lack of independent verification of previous or future eye care visit scheduling or previous DR findings. While DR may have progressed since the last exam recalled by the person with diabetes, the rate of progression from no retinopathy to vtDR within 1 year has been found to be low, at 1.5–3.0% (10,11), and thus would not explain the high proportion (55%) with vtDR in the study who were unaware of any DR. From a positive health behavior perspective rather than a health literacy perspective, participants reported more frequent previous eye exams and shorter intervals between follow-ups than people with diabetes whose DR status was mild or none. Awareness of DR and vtDR were more likely if the people with diabetes were seeing a more specialized eye care professional. It is also possible that those who accessed care with a more specialized eye care professional may have chosen the professional because they were more aware of their risk for DR.

HCP need to educate people with diabetes about eye care awareness and share screening guideline recommendations and findings with people with diabetes, and obstacles to appropriate eye care access need to be addressed (Fig. 1). The study participants were likely highly motivated, given that they attended a specialist diabetes center. Others have found that indeed those with more severe DR were more likely to be aware they had DR than those who had mild or no retinopathy despite low health literacy (12). The Joslin cohort may have more health literacy than the general population with diabetes, which suggests that recall of DR severity may be even less accurate in more general community settings.

Screening guidelines are based on evidence and consensus, which change. The current study compares follow-up concordance with the recommendations of the American Academy of Ophthalmology for follow-up intervals of 12 months, 6 months, 3 months, and 1 month for increasing severity of DR (13). Adherence will depend on agreement of the HCP, the eye care professional, and the person with diabetes with screening recommendations. There has recently been further rationalization of screening recommendations from universal recommendations of annual screening or more frequent intervals because of the large number of negative screens. Strategies to individualize screening have been recommended based on findings in children with diabetes and other age-groups (14,15). Calls to extend the screening interval to 4 years for those with no retinopathy and to 3 years for those with minimal background retinopathy have occurred based on findings from the Diabetes Control and Complications Trial (DCCT)/Epidemiology of Diabetes Interventions and Complications (EDIC) (16). For those who have achieved very low glycemic targets since diagnosis, the risk of vtDR is greatly reduced, with a threshold below which it may not develop until 24 years’ duration of type 1 diabetes (17). Conversely, we need to also be aware of health care discrepancies and recognize that those at highest risk have lower uptake of screening (18). Algorithms for individualizing screening have been developed (19,20), suggesting that intervals between screenings could be personalized based on additional data rather than simply DR status at the last screening. A recent real-world retrospective review found the “low risk” people with diabetes who would have adverse outcomes with biennial screening compared with annual screening; however, these individuals were mainly younger adults and members of ethnic minority groups (21).

The authors declare no conflicts of interest and argue for adherence to pupillary dilation as per guidelines. For this study, they used low light nonmydriasis for the retinal imaging. Current global guidelines continue to recommend mydriatic photography, but nonmydriatic ultrawide-field retinal photography is increasingly used, as it may detect more peripheral DR lesions than traditional 7-field retinal photography (22). As it can often be performed without the need for mydriasis, this may make screening more acceptable, quicker, and safer for people with diabetes. Future technological developments that may significantly affect DR screening include handheld digital cameras, teleophthalmology, and artificial intelligence, which could play major roles particularly in resource-limited settings (23).

DR screening is a large burden on the health care system. More importantly, it is a burden for the person with diabetes. Several questions related to improving DR screening rates remain unclear. These include whether screening increases or decreases the anxiety of managing diabetes and whether self-awareness of DR increases or reduces motivation to manage this chronic, complex disorder. The current study also suggests that denial of DR awareness may be a coping strategy. There are limited data on whether finding complications leads to changes in health behavior and improvement in measures of glycemic control (24). We need to understand more so we can help all people with diabetes prevent vision loss.