Incidence and seasonality of major ocular trauma: a nationwide population-based study

We designed this study to identify the epidemiological characteristics and trends of various types of ocular trauma in the population of the Republic of Korea. We conducted a nationwide, population-based, cross-sectional study using the Korean National Health Insurance claims database for January 2010 to December 2018. We compiled the monthly numbers of patients diagnosed with hyphema and those who received open reduction surgery due to orbital blowout fracture (BOF), primary closure of the cornea or sclera (PCCS), or intraocular foreign body (IOFB) removal. We obtained annual and monthly incidence rates, and differences according to age, sex, yearly trends, and seasonal variations. The incidence rate (per 100,000 person-years) was high in the order of hyphema (18.43), BOF (11.58), PCCS (1.99) and IOFB removal (0.39). Male predominance was evident in all types of major ocular trauma, but the age distribution varied with the type: hyphemas were most prevalent at 10–14 years of age, BOFs at 25–29 years of age, and open globe injuries (OGIs) at age 60 and older. Although all types of trauma showed significant seasonality, hyphemas (amplitude: 174.81) and BOFs (23.17) showed higher amplitudes compared to OGIs (PCCS: 11.96; IOFB removal: 6.72). While the incidence of blunt trauma injuries, including hyphemas and orbital BOFs, decreased steadily from 2010 to 2018, that of OGIs showed no remarkable change.

open globe injury. The

Discussion
In this nationwide population-based study of ocular trauma, highest incidence rates were shown in hyphema, BOF, and OGI respectively in descending order. We confirmed the male predominance of all major types of ocular trauma 1,13,14 , and found clear seasonality in each type of trauma; however, the yearly trends, age distributions, and amplitudes of periodicities differed depending on the type of trauma. To date, ocular trauma has been thought to occur most at relatively young ages 1, 11, 12, 15 , but we found different patterns of age distribution, depending on the type of ocular trauma: hyphema was most prevalent at 10-14 years of age, BOFs at 25-29 years of age, and OGIs at ≥ 60 years of age. Previous studies indicated that hyphema mainly occurred at the ages of 5-14 years during participation in sports, while BOFs occurred among those in their 20 s and 30 s as a result of violent assaults, traffic accidents, and sports 12, 16, 17 . We found a higher incidence of OGIs in relatively old patients, which was presumably due to deteriorated physical ability and delayed reaction to accidents.
Although all types of trauma showed significant seasonality, hyphemas (amplitude: 174.81) and BOFs (23.17) showed higher amplitudes compared to OGIs (PCCS: 11.96; IOFB removal: 6.72). Specifically, blunt trauma injuries including hyphema and BOF had peaks between May and October, a period associated with increased participation in outdoor activities. However, OGIs, including PCCS and IOFB removals, showed less seasonality, probably because of the high relevance of occupational accidents 18,19 .
The incidence of hyphema and BOFs declined between 2010 and 2018. This may have been due to the development of safety measures in the Republic of Korea that included increased use of eye protection during outdoor activities. However, the incidence of OGIs did not decrease over the period. Furthermore, in contrast to closed globe injuries, OGIs can result in permanent visual impairment through endophthalmitis, traumatic cataracts, retinal detachment, and corneal opacity. Thus, increased efforts to prevent OGIs are needed.
We suggest that prevention strategies based on age or type of injuries to be considered. For pediatric ocular injuries, prevention system or education program to avoid accidents in potentially dangerous activities should www.nature.com/scientificreports/ www.nature.com/scientificreports/ be implemented 20 . Parents or teachers have to play an important role in supervision 6 . To reduce ocular injury by traffic accidents, enhancement of legal sanctions including enforcement of seatbelt laws or development of automotive technology for safety are required. Additionally, in workplace, efforts such as enforcing to wear preventive equipment or advancement of technology to reduce unintentional accidents should be made. There were some limitations to this study. First, we could not identify the exact cause of each ocular trauma. Second, we inferred the incidence rates of BOFs and OGIs, based on the numbers of surgeries. Thus, the incidence rates of BOFs and OGIs may have been underestimated. However, our data for 50 million Korean residents with a single NHI system with affordable medical costs likely reflected actual incidence rates, with minimal chance of selection bias 21 .
In conclusion, in this nationwide population-based study, we investigated the incidence rates and seasonality of four major types of ocular trauma in the Republic of Korea from 2010 to 2018. All of them showed male predominance, but each showed different age distributions. While the incidence of blunt trauma injuries such as hyphemas and BOFs decreased, that of OGIs did not decrease. Based on these results, more research is needed to determine the causes of ocular trauma and to establish appropriate prevention policies.

Methods
Study design and database. We conducted a nationwide, population-based, cross-sectional study using the Korean NHI claims database for January 2010 to December 2018. This study was approved by the Institutional Review Board of St. Vincent's Hospital (VC19ZESI0179). All Korean residents must enroll in the NHI system, so this database encompasses all medical claims in the Republic of Korea. We identified all patients who received a principal diagnosis or corresponding surgery in one of the following: hyphema (International Classification of Diseases, 10th revision code H210), reduction of orbital BOF (S5211), PCCS (S5380), and IOFB removal (S4891 or S4892). In cases of hyphema, only newly diagnosed cases were included in the study. The numbers of patients diagnosed or treated with each disorder each month and year were collected. Statistical analysis. We calculated incidence rates depending on year, sex, and age group, and determined the differences among them. We acquired incidence rate based on census population data of each group obtained from Statistics Korea. Mann-Whitney U-test was employed to compare average annual incidence rates between male and female. In addition, the cosinor test was used to examine seasonal variation based on monthly incidence rates 22 . All analyses were conducted using R software, version 3.6.1 (R: A Language and Environment for Statistical Computing, R Core Team, R Foundation for Statistical Computing, Vienna, Austria (2019) https :// www.R-proje ct.org).

Data availability
The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request. Figure 2. Comparisons of incidence rates by age distribution in males (red) and females (green). The highest incidence of hyphemas (A) was in patients aged 10-14 years, for both sexes, and the highest incidence of open reductions of orbital blowout fractures (B) was in patients aged 25-29 years, for both sexes. The incidence of open globe injuries (C, D) peaked in males at 60-64 years of age, whereas that of females increased with age.