Epidemiological Association Between Systemic Diseases and Keratoconus in a Korean Population: A 10-Year Nationwide Cohort Study

Purpose:To investigate the association of systemic diseases with keratoconus in the general Korean population.Methods:This is a nationwide population-based retrospective cohort study using the Korean National Health Insurance Service-National Sample Cohort database from 2002 to 2015, involving 1,108,369 individuals. Patients with keratoconus were identified using the Korean standard classification of diseases code H18.6. The prevalence and annual incidence rates were estimated. To examine the risk factors, 5 controls were matched per patient with keratoconus by propensity score matching using age and household income. Univariate and multivariate regression analyses were performed to assess the association between relevant factors and keratoconus.Results:A total of 613 subjects were identified as patients with keratoconus from the cohort database. The prevalence rate was 55.31 cases per 100,000 people [95% confidence interval (CI): 51.01-59.86]. The annual incidence rate, calculated using a predate 1-year washout period, was 4.47 cases per 100,000 person-years (95% CI: 4.11-4.85). People with allergic conjunctivitis had a 37% increased odds of being diagnosed with keratoconus [odds ratio: 1.37 (95% CI: 1.12-1.67), P = 0.002] compared with those without allergic conjunctivitis. By contrast, people with allergic rhinitis had a 52% reduced odds of being diagnosed with keratoconus [odds ratio: 0.48 (95% CI: 0.38-0.59), P < 0.001]. Atopy and eczema, asthma, connective tissue disorders, diabetes mellitus, sleep apnea, and inflammatory bowel disease had no significant association with a positive keratoconus diagnosis.Conclusions:Allergic conjunctivitis may increase the risk of developing keratoconus in Koreans.