Public health and the eyePrevalence and risk factors of pterygium: a systematic review and meta-analysis
Introduction
Pterygium, one of the most common eye disorders, is the growth of subepithelial fibrovascular tissue starting from the bulbar conjunctiva onto the cornea.5 Esthetic concerns, irregular astigmatism, and decreased vision are important issues associated with this disease.14, 42 Long-term exposure to ultraviolet light from the sun is the most important risk factor for pterygium4, 24, 56, 65; however, other factors such as low income, smoking,56 region of residence (urban and rural), older age,9, 70 male gender, latitude,34 and farming41 are other possible risk factors. Because of variations in the studied age groups and study settings (population-based vs clinic-based studies), the prevalence of pterygium in surveys conducted in different parts of the world ranges from 1.3% in the Tehran Eye Study15 to 53% in Taiwan.63 Despite the various studies performed to determine the type and amount of the effect of each causative factor, estimates differ among studies and in some cases arrive at opposite results. The purpose of the present meta-analysis is to provide an accurate estimate of the prevalence of pterygium and to identify its determinants using a combination of all clinical and population-based studies from around the world.
All stages of this study were performed in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The criteria for including studies into the meta-analysis were: being designed as an observational epidemiological study such as cross-sectional, case-control, cohort, population based or clinic based; providing a transparent report of the prevalence and odds ratio (OR) for obtaining combined indices of prevalence and OR. Among studies conducted on the same population, the one with higher quality was included. Articles that did not meet any one of these inclusion criteria were excluded.
The outcome measures included the prevalence of pterygium and its risk factors such as alcohol consumption, smoking, outdoor occupation, region of residence, sunlight exposure, use of sunglasses and hats, age, and gender. To determine the prevalence of pterygium, we included all studies reporting the overall prevalence of pterygium or broken down by age and gender. Studies that defined exposure to alcohol and smoking as consumers and nonconsumers were included in the final analysis. In addition, given the small number of studies that defined smoking and alcohol as current users, these were allocated to the consumer group. We used indoor and outdoor categories to determine the effect of occupation environment. Region of residence included urban and rural categories. Sunlight exposure, according to extracted data, was classified into 2 groups of under and over 5 hours of exposure. Age was grouped into 10-year intervals.
To ensure the proper selection of articles in terms of their pertinence to the research subject and meeting the inclusion criteria, 2 researchers (E.H. and M.S.) independently reviewed the articles. The names of the authors, journal title, and the results were not concealed from the reviewers. If there was any dispute, a decision was made through negotiation or consultation with a third person. The Kappa percentage for the interreviewer agreement was 74.5%. The variables taken in consideration in this review included the name of the first author, year of publication, country and city of the study, the mean age of the studied sample, gender, study design, type of population studied, region of residence (village, town), occupation, alcohol consumption, smoking, level of exposure to sunlight, and wearing hats and sunglasses in the sun.
We used the STROBE checklist for cross-sectional, case-control, and cohort studies to assess the quality of the studies in terms of methodology and reporting.
Statistical heterogeneity of the studies was assessed using the chi-square test at a significance level of 5%. To quantify heterogeneity among results, we used the I-square statistic and Higgins classification, based on which, an I-square value more than 75% can be considered as heterogeneity.
The summary measures of this study included the prevalence and the OR of developing pterygium in the presence of risk factors as an index of correlation; these were calculated along with 95% confidence intervals (CIs) for a 2-tailed distribution.
Data analysis was done using the Stata (version 11, StataCorp, College Station, Texas) and applying the random effects model at a 95% confidence level.
Section snippets
Results
A total of 3255 articles were identified; 3155 were found through database search, and 100 through scanning reference lists and other sources. After eliminating duplicates, the titles and abstracts of 3055 articles were studied, and after applying the exclusion criteria, 2745 articles were excluded, and the full text of 310 articles was reviewed. After assessing the quality of the selected articles based on Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, 247
Discussion
Although numerous studies around the world have assessed the prevalence and determinants of pterygium, given the large variation among study results, particularly prevalence estimates of the disease, it is necessary to conduct a comprehensive meta-analysis study of this disease after the first one in 2013 by Liu and coworkers.34 Our findings showed a combined prevalence of 12% for pterygium in the world. The lowest reported prevalence was 0.07% in the study by Alqahtani and coworkers2 in Saudi
Conclusion
The present study is the second meta-analysis since 2013 on the prevalence and risk factors of pterygium in the world. Through a review of 68 articles, the global prevalence of pterygium was found to be 12%. In accordance with epidemiological studies with proper sample sizes, it was demonstrated that pterygium is more prevalent among men and in older age groups. Older age, male gender, outdoor occupations, and rural residence are the most significant demographic risk factors. Sunlight exposure
Disclosures
The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.
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