The effect of altitude on the incidence of keratoconus in Israel-a population-based study.

OBJECTIVES: To evaluate the correlation between residential altitude and keratoconus incidence in Israel, considering potential ethnic variations. METHODS: This retrospective population-based study analysed data from Israel's largest healthcare provider from 2005 to 2020. Keratoconus patients were identified using ICD-9 codes. Annual keratoconus incidence was calculated for three residential altitude groups: below 0 m, 0-500 m, and above 500 m. To address ethnic confounding, keratoconus prevalence rates in 2019 were analysed across altitude groups for both the total population and the Jewish subgroup, Israel's largest ethnic group. RESULTS: The study population increased from 3,440,265 individuals in 2005 to 4,316,825 in 2020. Among 14,769 keratoconus patients (mean age: 35.19 ± 13.3 years), the average incidence was 24.04 per 100,000 individuals. Annual keratoconus incidence increased significantly with altitude 17.01, 23.73, and 26.63 per 100,000 individuals in regions below 0 m, 0-500 m, and above 500 m, respectively (0 < 0.05). In 2019, total prevalence rate was 0.40%, increasing with altitude: 0.37%, 0.43%, and 0.56%. The Jewish population exhibited a similar pattern: 0.35%, 0.39% and 0.56%. Logistic regression analysis revealed significantly higher odds of keratoconus above 500 m compared to lower altitudes in both populations (p < 0.05). CONCLUSION: A positive correlation was identified between altitude and keratoconus incidence and prevalence in both the total population and the Jewish subgroup. These findings indicate altitude may be a significant risk factor for keratoconus, warranting future investigation.