Conclusions
In our sample, rates of adherence to follow-up DFE recommendations were disappointingly low across all ages and ethnic groups, ranging from 35% to 65% adherence depending on the severity of DR. Longitudinal utilization was also below recommendations, with the annual DFE rate being substantially less than 1 DFE per year for patients with mild and moderate DR and less than 2 DFEs per year for patients with severe DR.
For over two decades, it has been well known that early identification and treatment can prevent at least 50% of severe vision loss in patients with DR.28 Previous studies have evaluated eye care utilization associations on a population level based on self-reported data, but this is the first study to analyze clinical and demographic characteristics of patients who do and do not adhere to follow-up DFE guidelines in a large, urban academic setting. This is also the first study to examine DFE adherence by severity of DR and the individual, clinical, and system-level factors that impact longitudinal utilization of DFE services.
Statistically significant variables after adjustment
Our results indicate that severity of DR is independently and strongly associated with adherence to timely DFEs. Specifically, patients with mild or no DR were the least likely to adhere to follow-up recommendations. We hypothesize several reasons for this association. First, patients with mild DR might not seek regular ophthalmic care because of a lack of perceived need—particularly because visual symptoms may be minimal or absent and lower severity of DR is associated with fewer systemic manifestations.29 In addition, up to half of individuals with moderate-to-severe visual loss do not seek regular eye care because they do not perceive a need for care.18 30 It is also possible that patients in our study with mild or no DR had less contact with medical professionals perhaps due to being generally younger and having less time available due to competing commitments (eg, work or family). Thus, they may have less encouragement to regularly follow-up with their eye care provider. Lastly, there could be other factors not yet explored. Therefore, this association identifies a population that can be targeted with educational interventions to increase rates of eye care utilization among people with diabetes.
Population-based studies have consistently found diabetic eye care utilization to be associated with visual impairment.12–14 In our population, after adjusting for known risk factors, patients with visual impairment were more likely than patients with normal vision to adhere to initial follow-up DFE recommendations and use DFE services longitudinally. Presumably, visual loss motivates patients to obtain eye care.
Our study is also the first to find a relationship between smoking status and adherence with diabetic eye care: smokers were less likely than non-smokers to adhere to the recommended DFE follow-up and smokers had lower longitudinal utilization of DFE services, even when controlling for other variables. Smoking is related to multiple microvascular complications of diabetes, although smoking’s specific effect on retinopathy has not been well defined.31 Smoking has also been directly linked to two of the leading causes of vision loss, cataracts, and macular degeneration,32 and may contribute to glaucoma.33 Smokers have been shown to use more healthcare services at a higher cost than non-smokers, which is in contrast to our findings of lower eye care utilization among individuals with diabetes who smoke.34 It is unclear why smoking is independently associated with less follow-up adherence. Perhaps, patients who smoke have other symptomatic health problems which patients give priority over asymptomatic or less symptomatic ocular disorders. People with diabetes who smoke may place less value on eye care given that smokers have worse overall health compared with non-smokers, leading to other illnesses superseding the perceived need for eye examinations.35 Smokers also tend to be less educated than non-smokers and may not understand the importance of known health recommendations, which may contribute to the differences between the groups.36 Additionally, self-management of diabetes is difficult, as attested to in multiple studies and addictions such as nicotine may impact self-management strategies.
Whether or not self-reported HbA1C or blood glucose was mentioned in a patient’s chart was found to be significantly associated with DFE adherence rates and with increased longitudinal utilization, which was unexpected.37 Since HbA1C and blood glucose were from patient’s self-report, it is possible that these patients are, in general, more informed and involved in their healthcare and therefore more likely to adhere to recommendations. However, since three-quarters of our patients were missing HbA1C values and one-third of patients were missing blood glucose, we did not evaluate relationships between level of HbA1C or blood glucose and adherence or other variables. While an objective marker of diabetes control would have been useful, the data could not be correlated with actual HbA1C or blood glucose, as it was subject to recall bias.
Caucasian ethnicity has been associated with higher rates of DFEs compared with African-Americans and Latinos with diabetes,10 13 14 16 18 which is particularly concerning as African-Americans and Latinos are projected to have the largest increase in prevalence of diabetic eye disease.6 However, ethnic status has not been found to be independently associated with DFE rates in all studies.11 In this current investigation, there was only an association between ethnicity and longitudinal utilization in patients with mild DR, with Asians having the most DFEs per year. Adherence to follow-up recommendations was consistently low across all ethnic/racial groups as shown in table 2.
Non-statistically significant variables after adjustment
Insurance status is another variable that has been associated with DFE rates in population studies with sizeable proportions of patients without insurance status or access to free care.12 16–18 21 24 One study also found that among individuals with diabetes over 65 years of age, people who were dual eligible for Medicare and Medicaid were significantly less likely to receive DFEs compared with people eligible for Medicare alone (63% vs 75%; p<0.0001).20 We found insurance status to be associated with adherence rates and longitudinal utilization in the univariable analysis, with Medicaid patients having the lowest adherence rates and Medicare patients having the highest adherence rates. However, this association was not significant in multivariable analyses.
Several previous studies have found higher socioeconomic status (SES) to be associated with having DFEs.11 12 24 In a national representative sample of 84 572 people, Brechner et al found that in people with insulin-dependent diabetes and annual incomes over US$40 000, 72.9% had DFEs within the last year compared with 32.4% of people who had annual income less than US$10 000.11 We found SES was only associated with longitudinal utilization in patients with mild DR, not in initial DFE follow-up, and that patients of the two lower SES brackets had the most DFEs per year. Our findings could be real or due to the fact that we imputed SES using each subject’s census tract location and dividing the census tracts for our patients into four quartiles based on relative SES. While this method for estimating SES has been previously validated, it is limited by relying on a patient’s address and it cannot differentiate SES of individual people living in the same census tract.
Gender has been significantly associated with different DFE rates in a number of studies, with women consistently having higher rates of eye care compared with men.12 14 16 This difference has been attributed to perceived need of care by each gender. According to the Behavioral Risk Factor Surveillance System, 42% of men with moderate-to-severe vision loss reported no need to have an eye examination compared with 29% of women with similar vision loss.22 However, our study found no differences in initial follow-up or eye care utilization between men and women. Our results agree with a recent study from Paskin-Hall et al, who also found gender was not significantly associated with annual DFE adherence.24
Distance from a healthcare facility or provider can be a barrier to care. Increased driving distance has been associated with poor glycemic control38 39 and lower use of insulin.40 One study found that people residing more than 10 miles from a diabetes management center were almost twice as likely to have HbA1C >7% compared with people living closer to the care center.39 In contrast, we only found an association between driving distance and longitudinal utilization in severe patients, with patients living 5–25 miles within our healthcare facility having the most DFEs per year. Patients living within 5 miles of our facility are more likely to be from medically underserved areas than patients living slightly further away. In addition, our population was in an urban area with a large public transportation system. Previous studies linking driving distance to decreased care utilization have been predominantly conducted in rural areas where public transportation is minimal or absent.
Strengths and weaknesses
The strengths of our study include the large urban population followed over 4 years, the ability to determine DFE adherence based on objective data rather than self-report, and the ophthalmology clinical setting, which has not been previously characterized in terms of factors associated with adherence to follow-up eye care.
Weaknesses of our study included limited data concerning self-reported HbA1C levels and ethnicity, although we were able to impute ethnicity using a validated method.27 Another potential weakness is that we were only able to capture DFEs at our clinics. It is possible that some patients received follow-up eye care outside our clinics that was not captured in our data. Finally, although we attempted to gather extensive patient information, as an observational study, there is a potential for unmeasured confounding of associations.
The results of this study have important clinical and public health implications. Primary care practitioners, diabetic specialists, and eye care providers in urban clinical settings should identify people with diabetes at risk for poor follow-up in order to improve adherence rates, particularly:
patients with normal vision;
older patients with severe DR;
patients with mild DR and no history of other eye diseases;
patients with no ophthalmology documented HbA1C or blood glucose;
smokers.
Population-based health programs can also target this cohort with specific educational interventions in order to increase eye care utilization among people with diabetes and attenuate the potential for severe visual disability from DR. While all patients with diabetes need to improve follow-up, targeting subgroups with low adherence rates could have a high impact and prevent progression to more severe DR.