Global Prevalence of Keratoconus in the Adult Population: A Systematic Review

Abstract

To synthesize contemporary estimates of adult keratoconus prevalence worldwide and determine how geography, demographics, and study methodology shape reported rates. We systematically reviewed original studies (2019–2024) quantifying keratoconus in adults. We excluded paediatric-only reports and studies focused solely on treatment, transplantation, or non-epidemiologic associations. We extracted population frame (general population vs. refractive-surgery candidates), diagnostic approach (administrative registry coding, corneal topography, Scheimpflug tomography), and sex distribution. Prevalence was recorded per 100,000 persons and incidence per 100,000 person-years. Twenty-five studies met inclusion criteria. In general populations, prevalence ranged from 4.29 per 100,000 (Taiwan, 0.0043%) to 13,700 per 100,000 (South Africa, 13.7%). Incidence—reported in a subset—spanned 1.56 to 28.47 per 100,000 person-years. Male predominance was frequent but heterogeneous (male-to-female ratios ~ 0.57–3.61). Studies of refractive-surgery candidates showed substantially higher prevalence (typically 1.6%–21.7%), consistent with selection of young, myopic cohorts and the use of sensitive tomographic screening. Reported prevalence of keratoconus in adults varies markedly worldwide and is strongly influenced by study methodology, diagnostic criteria, and population characteristics. Standardized tomographic diagnostic protocols and prospective population-based studies are needed to improve the accuracy and comparability of global epidemiological estimates.