Prevalence of DR presents large variations amongst different ethnic groups worldwide [6, 18]. A vast number of studies estimating the extent and associated risk factors created a strong basis for the design of screening programs aiming towards the prevention of vision-threatening conditions arising from DR [19]. The role of ethnic or population differences as a significant co-factor for the variability of DR globally was previously investigated [20–22]. These epidemiologic data could be attributed to differences in the socioeconomic status, lifestyle preferences and healthcare accessibility and also to the suspected role of the genetic background. Over the last decade, a large number of genetic studies has revealed genetic loci strongly related with the development and/or progression of DR, thus setting the stage for an ever-growing role in terms of genetic susceptibility research [23–25]. Greek ethnicity has drawn a significant amount of interest after the presentation of its cardioprotective effect in the Seven Countries study [26] and a number of publications followed pointing the favorable combination of Mediterranean lifestyle and genetic background in cardiovascular diseases [11, 27, 28]. In the context of investigating the role of Greek ethnicity in microvascular entities, Brazionis et al., 2010 presented a lower prevalence of DR in Greek-born Australian citizens (23%) compared to the Australian-born sub-cohort (37%) and also that Greek ethnicity presented 68% lower odds of DR, after the adjustment for demographic and clinical variables [12]. However, to date there are no published studies available concerning the prevalence of DR in the Greek population.
The current study is the first one to present the extent and severity of DR and DME in a Greek cohort and also identify associated risk factors. The prevalence of DR was estimated at 38.7%, DME at 6.3% and PDR at 5% of the participants. As far as the severity is concerned, the majority of patients diagnosed with signs of DR presented with mild NPDR (20%), 9% had moderate and 4.7% had severe NPDR and 5% presented with PDR. Additionally, the proportion of patients subjected to PRP and/or intravitreal administration of anti-VEGF was as low as 5.3% and 7%, respectively (Table 1).
A recent meta-analysis by J. Q. Li et al., 2019 presented the overall prevalence of DR and DME in Europe, extrapolating data from 35 studies that involved 205,743 patients in total [29]. The prevalence of any DR was 25.7% in both DM type I and type II, while therapeutic interventions due to PDR or DME were required in 2.2% and 3.7% of the patients, respectively. The majority of studies involved northern and southern European registries, followed by western and finally eastern Europe that included only one publication available from Hungary. The reported prevalence of DR was significantly elevated in northern (29.6%) and southern (25.8%) registries, followed by eastern (20.1%) and western (18.3%) Europe. In the same study, meta-analysis and meta-regression analysis by country presented that higher rates of DR were recorded in Italy (34.8%), UK (29.8%) and Spain (26.5%) followed by Germany (21.0%) and France (14.6%). According to our findings, the prevalence of DR and DME in Greek diabetic patients is similar to the ones recorded in Italy, where DR and DME were 34.8% and 4.6%, respectively. This finding could be attributed to the fact that these two countries share similarities in terms of lifestyle, dietary preferences and healthcare accessibility. The percentages of DR and DME recorded from Italy and from our Greek cohort are strikingly higher compared to the results presented from the rest of the European countries included in the meta-analysis from J. Q. et al., 2019 [29]. The validity and accuracy in these studies are strongly associated with the sources available for data collection in each country. In the UK, the majority of patients are registered in a national screening program while in Spain community eye clinics are responsible for the follow-up visits of all diabetic patients thus providing a large amount of data. In the rest of the European countries, including Greece, there are no official screening programs for DR and the information required is recorded mostly from patients that were either referred from another healthcare professional or patients seeking medical advice due to symptoms associated with DR. Therefore, the interpretation of these data as population-based should be considered with caution.
Previous studies in different populations around the globe have revealed a number of potential associations between DR and variables that concern demographic, socioeconomic and clinical aspects of each ethnic group [30–33]. Binary logistic regression analysis in this Greek cohort identified longer duration of diabetes (p=0.000), poor glycemic control (p=0.033) and lipid metabolism disorders (p=0.001) as significant risk factors for the development of DR (Table 2). Also, distinct binary logistic regression analysis for DM type II patients revealed that duration of diabetes (p=0.000), elevated levels of HbA1c (p=0.035) and hypertriglyceridemia (p=0.002) along with age (p=0.001) are potential risk factors for the development of any stage of DR in these patients (Table 5). In the group of patients with DM type I, there was a statistically significant difference in the prevalence of DR in older patients (p=0.031), although this was not confirmed in binary logistic regression analysis (p=0.746) (Table 4). No further statistically significant differences were identified in this group, possibly due to the restricted number of patients included (n=21). Hypertension and hypercholesterolemia were previously identified as the most common modifiable risk factors for DR [34–36]. However, in the current analysis these variables did not present a statistically significant association with the development of DR in the total cohort (Table 2) as well as in the subgroup analyses conducted for DM type I (Table 4) and DM type II patients (Table 5).
There are several limitations in our study. Grading of DR was assessed only through detailed clinical fundus examination due to limitations concerning the availability of imaging equipment. Also, the number of patients with DM type I was low, thus restricting the statistical analysis for the investigation of potential risk factors in this group. Finally, patients included in this cohort were referred to the medical retina clinic by other healthcare professionals or were self-referred due to the lack of a national screening program. Therefore, any extrapolation of our results to the Greek population should be done with great caution.
In conclusion, this is the first attempt to assess the prevalence of DR and DME and study associated risk factors in a cohort of Greek diabetic patients. Our findings are in consistency with previous results from studies of various ethnic populations presenting risk factors for the development of DR globally [6, 20, 33, 37–39]. Our study demonstrated that duration of DM is a significant factor that should be taken under consideration in the design of a national screening program for DR. Additionally, we found that both HbA1c and hypertriglyceridemia were significantly associated with DR and being modifiable risk factors, they could serve as important educational points for both healthcare professionals and patients. Taking under consideration the continuously increasing prevalence of DM and the significant financial burden in global healthcare, the current study aims to enrich the current statistics on DR and DME in Europe and create a base for further studies in the Greek population.