Association between outpatient visits for pterygium and air pollution in Hangzhou, Chinaā
Graphical abstract
Introduction
Air pollution has increased with civilization and industrialization, and this has had detrimental effects on people's health, especially those living in developing countries with severe air pollution conditions (Bai et al., 2018). As the largest developing country in the world, China is undergoing rapid social and economic development, which has resulted in the deterioration of the environment and caused many health-related issues for its population (Bai et al., 2018; Guan et al., 2016). Society and the government are therefore paying increasing attention to the relationship between air pollutants and certain diseases, their pathological mechanisms, and appropriate treatments. Several studies have demonstrated that an increase in air pollution is significantly associated with the development of diseases related to many systems, including the cardiovascular, respiratory, and nervous systems (Babadjouni et al., 2017; Franklin et al., 2015; Guarnieri and Balmes, 2014; Mo et al., 2018). As one of the two organs directly exposed to air conditions in humans, the eyes are highly vulnerable to various air pollutants (Jung et al., 2018). Evidence has shown that air pollution may induce or aggravate various eye diseases, such as dry eye syndrome and conjunctivitis (Fu et al., 2017b; Mandell et al., 2020; Mo et al., 2019). However, whether the incidence and recurrence rates of pterygium are influenced by air pollution remains unclear.
Pterygium is a very common ocular disease defined as a fleshy mass of thickened conjunctiva that grows over part of the cornea, usually from the inner side of the eyeball, and causes visual disturbances (Liu et al., 2013). It is characterized by abnormal epithelial cell proliferation, vascularization, and invasion of the corneal epithelium. Several studies have suggested that the risk factors for pterygium are racial differences, older age, male gender, outdoor occupations, living in a rural environment, and ocular demodicosis (Lin et al., 2019; Song et al., 2017). However, the effects of air pollution on the formation and development of pterygium remain controversial. Peruvian researchers conducted a study of workers who produce toilet paper in an environment with high levels of particulate matter (PM) and found no association between ocular exposure to PM and the development of pterygium (Ramirez et al., 2018). In contrast, in a two-year population-based cross-sectional study in Korea (Lee et al., 2017), found that exposure to higher PM10 levels was associated with primary pterygium, although no association between PM10 and overall pterygium or pterygium recurrence was observed. Additionally, sawmill workers who were exposed to airborne soil were also found to be at risk of developing conjunctival disorders, including pterygium (Njinaka et al., 2011). More studies are, therefore, needed to understand the relationship between air pollutants and pterygium and explore the specific pathological mechanism of pterygium.
The formation and recurrence of pterygium are quite complicated, involving multiple processes and both genetic and environmental risk factors (Ang et al., 2012; Cardenas-Cantu et al., 2016; Rezvan et al., 2018). Although the onset of pterygium is unclear, evidence has shown that reactive oxygen species and chronic inflammation induced by ultraviolet light and other environmental factors (e.g., humidity), as well as other risk factors, are the main causes of pterygium formation (Cardenas-Cantu et al., 2016; Sacca et al., 2013). Our earlier epidemiological studies have shown that increases in many air pollutants are associated with outpatient visits for several ocular surface diseases, including dry eye syndrome and conjunctivitis, and that chronic inflammation plays a key role in the pathological mechanism (Fu et al., 2017b; Mo et al., 2019). These results are consistent with those of other studies (e.g., Ma et al. discovered higher levels of IL-6 and IL-8 in dust-treated human corneal epithelial cells; (Xiang et al., 2016). Additionally, some studies have reported that severe air pollution may also increase the number and density of goblet cells in the conjunctiva (Torricelli et al., 2014). However, whether air pollutants are associated with the onset and recurrence of pterygium and which specific air pollutants are involved have not yet been established.
In the present study, a time-stratified case-crossover design was applied based on the outpatient visit data for pterygium at the Eye Center of the Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China, and the concentrations of air pollutants in the same city from July 1, 2014, to November 31, 2019, to investigate the association between air pollutants and pterygium as part of our series of epidemiological studies on the effects of air pollution on ocular diseases.
Section snippets
Patient information
Daily outpatient information (nĀ =Ā 84,571) comprising each patient's unique number, visit dates, age, gender, and residential address was obtained from July 1, 2014, to November 31, 2019, from the Eye Center of the Second Affiliated Hospital of Zhejiang University School of Medicine, which is the largest eye clinic in Zhejiang Province in Southeastern China. Patients (nĀ =Ā 3017) who were diagnosed with primary pterygium (ICD-10 code H11.000) on the first outpatient visit and for whom no
Results
A total of 3017 outpatients who were diagnosed with primary pterygium on the first visit to our eye center from July 1, 2014, to November 31, 2019, were included in the present study. Among these were 1545 (51.2%) males and 1472 (48.8%) females. In terms of age, 2147 (71.2%) patients were younger than 65 years. No seasonal differences were observed, as 52.7% of the patients visited the hospital during the warm season. Patients who revisited the hospital after the first visit and were diagnosed
Discussion
A time-stratified case-crossover design was employed in our study to analyze the association between outpatient visits for pterygium and air pollutants based on the data of 3017 patients with primary pterygium. The results show strong associations between pterygium outpatient visits and various air pollutants, including PM2.5, PM10, SO2, and NO2.
Several studies have suggested that male gender is a risk factor for pterygium (Lee et al., 2017; Paik et al., 2019; Rezvan et al., 2018; Song et al.,
Conclusion
This study revealed positive associations between the air pollutants PM2.5, PM10, SO2, and NO2 and primary pterygium among outpatients in Hangzhou, China. Gender- and season-specific effects were observed between certain air pollutants and outpatient visits for primary pterygium, indicating a possible relationship between the incidence of primary pterygium and air pollution.
Credit author statement
Qiuli Fu: Conceptualization, Methodology, Investigation, Writing - Original Draft, Funding acquisition. Zhe Mo: Methodology, Software, Formal analysis, Data Curation, Writing - Original Draft. Yuzhou Gu: Validation, Writing - Review & Editing, Visualization. Bing Lu: Investigation, Data Curation. Shengjie Hao: Investigation, Data Curation. Danni Lyu: Investigation, Data Curation. Peiwei Xu: Methodology, Resources. Lizhi Wu: Methodology, Resources. Xiaoming Lou: Methodology, Resources. Hongying
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This work was supported by the National Natural Science Foundation of China [81670833, 81570822, 81502786, and 81870641], Zhejiang Province Key Research and Development Program [2019C03091 and 2017C03046], the Fundamental Research Funds for the Central Universities [2019QNA7026], the Science and Technology Program of Zhejiang [2014C03025], the National Natural Science Foundation of Zhejiang Province [LQ14H260003 and LY20H120010], Zhejiang Province Basic Public Welfare Research Project
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This paper has been recommended for acceptance by Payam Dadvand.
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Q.F. and Z.M. contributed equally to this work.