This study demonstrated an increasing trend in the incidence of RRD cases requiring surgery during the last decades in Korea. The incidence of RRD over a 5-year period in Korea has been previously reported  but it is difficult to grasp the trends due to the relatively short study duration. Therefore, this study was designed over a 12-year study period to estimate the trend of incident RRD cases requiring surgery.
The yearly standardized incidence rate of RRD cases requiring surgery was 9.78/100,000 person-years (95% CI, 9.70–9.86) in this study (Table 1). Our report showed a lower annual RRD incidence rate than those in previous nationwide studies, which were reported to vary from 8 to 16.4 [2,3,4,5,6,7,8,9,10] and which might be due to the slightly different definitions of RRD occurrences, data collection method, and regional and ethnic differences in each study.
The male preference observed in the RRD incidence, a male to female ratio of 1.20 in this study (Fig. 1B), coincides with that in the other studies [6, 19]. The prevalence of trauma and symptomatic posterior vitreous detachment (PVD) complicated by a retinal tear, which is more common in male patients, may have an influence on the higher RRD risk in male patients . The present study showed a bimodal distribution of the average RRD incidences with age over the 12-year study period; the highest peak being in the seventh decade of life and the second highest peak in the third decade (Fig. 1A). In each year from 2004 to 2015, the RRD incidence also demonstrated relatively constant highest and second highest peak age groups (Table 2). This result is consistent with our previous 5-year report in Korea and reports from other Asian countries on the incidence of RRD [6, 9, 10]. In the majority of studies, RRD incidence increases with age and shows the highest peak age of 50 to 79 years in both Caucasians and Asians [11, 19, 20]. PVD usually develops at 60 years of age and can play a critical role in the development of RRD. The volume of cataract extraction performed may partially affect the high RRD incidence rates in old age ; however, the second highest peak was clearly observed in Asians compared to Caucasians . Myopia was more frequent and more severe in Asians than in Caucasians, and the myopia-induced PVD in the relatively young age groups may be associated with the second highest peak incidence of RRD [21, 22].
The RRD incidence showed an increasing trend from 2004 to 2015 in the total Korean population. With age stratification in reference to 50 years, an increase in RRD incidence in patients of both sexes aged < 50 years was also observed. Nielsen et al. reported that the RRD incidence is increasing, and this increase is primarily driven by male patients aged ≥ 50 years using the Danish National Patient Registry data from 2000 to 2016 . However, in this study, APC in both male and female patients under 50 years of age (APC, 3.39; Fig. 2E and APC, 3.52; Fig. 2F, respectively) was much greater than that in male patients aged ≥ 50 years (APC, 1.71; Fig. 2H), which means that there is a trend with a similar increase in male patients aged ≥ 50 years in Asians compared to Caucasians, but among patients aged under 50 years, the RRD incidence in Asians showed a much greater increase than that in Caucasians. Myopia, a well-known risk factor for RRD, is increasing primarily in the young , especially in the Asian population. Korea is a country that has rapidly developed within a short period of time, and the increase in economic power and education level along with the body index, including body stature and body weight, can be attributed to the prevalence of myopia in the young age group, which is higher than that in the old age group . Kim et al. and Lee et al. reported that the prevalence of myopia in Korea has increased over time based on the database of the Korean National Health and Nutrition Survey 2008–2011 and the Korean Military Manpower Administration 2009–2013, respectively [24, 25]. The prevalence of high myopia also has increased in younger individuals [24, 26]. In addition, myopic eyes demonstrated a gradual increase in axial length over time , which can induce an increase in the risk of RRD. Another major risk factor for RRD is a pseudophakic eye after cataract extraction [14, 28]. With improvements in the technical difficulty and surgical safety of phacoemulsification for cataract extraction, the number of phacoemulsification has been increasing year by year, and cataract extraction tends to be performed at an earlier stage in Korea . Furthermore, in patients with high myopia, cataract surgery also tends to be performed at a younger age, and RRD as a postoperative complication after surgery is known to be more frequent .
In addition to the result of the joinpoint regression analysis, analysis of the 2004, 2009, and 2014 birth cohorts also showed a consistently increasing trend in RRD incidence in the same age group from 2004 to 2014 in the young generation under the age of 60 years in Korea (Fig. 3). In contrast, in participants aged ≥ 60 years, the RRD incidence rate increased in 2009 but decreased in 2014 on inspection of the 2004 birth cohort after 5 and 10 years. However, no statistically significant trend was found in people over 60 years old by the joinpoint regression analysis (Additional file 1 [Fig. S1D]). Partially, the population aged ≥ 50 years demonstrated a significant increasing trend from 2004 to 2007 unlike 2008–2014 and total period. Further analysis of this increase in early 2000s (2004 to 2007) may be necessary.
The limitation of this study is its nature based on claims database; hence, asymptomatic, unnoticeable or untreated RRD patients may exist by various factors such as old age, disease severity, socioeconomic status affecting healthcare service utilization, and systemic or ophthalmic comorbidity. These give rise to underestimate the RRD incidence. Furthermore, we were not able to access the hospital-based medical records of each patient for the severity and extent of RRD and the review of clinical data including myopia, pseudophakia, posterior vitreous detachment and other vision-devastating disease. Therefore, there is a limit to analyzing the association with RRD and these factors. In addition, since the database allowed for only 12-years of follow-up, we could only analyze three birth cohorts in each age group. Further investigation is needed to analyze the comprehensive birth cohort over a 40-years study period.
In conclusion, the current study showed an overall increasing trend in the incidence of RRD during the 12-year study period. As in Caucasians, the increase was observed in the total population in Korea. However, people younger than 50 years were considered to be important contributors to the increase in RRD incidence, unlike Caucasians. The increase in myopia and high myopia during the last few decades may play a role in this observation.