Rapid Growth and Persistent Geographic Concentration of Recorded Outpatient Corneal Cross-Linking Production in Brazil's Unified Health System, 2017-2025.

Background Corneal cross-linking (CXL) is the principal intervention used to stabilize progressive keratoconus. The procedure was incorporated into Brazil's Unified Health System (Sistema Único de Saúde (SUS)) in 2016 and became operational in national administrative systems in 2017. The geographic distribution of outpatient CXL production within the SUS has not been fully characterized. Objective To examine temporal growth, geographic distribution across federative units, geographic concentration, and the provider legal categories associated with recorded approved outpatient CXL production in the SUS from 2017 through 2025. Methods This nationwide ecological time-series study used public, aggregated data from the SUS Outpatient Information System (SIA/SUS). Approved quantities for procedure 04.05.05.040-2 were analyzed by processing year, federative unit, macroregion, and provider legal category. Indicators included annual volume, the number of active federative units, state and regional shares, the Herfindahl-Hirschman Index (HHI), effective number of federative units, Gini coefficient, and provider-category composition. Because 2017 represented a partial implementation year, long-term growth was assessed from 2018 to 2025. Analyses were descriptive and did not use inferential tests because the dataset covered the complete national aggregated series available for the procedure. Results A total of 12,216 approved outpatient procedures were recorded from 2017 to 2025. Annual production increased from 263 procedures in 2018 to 3,415 in 2025, a 12.98-fold increase corresponding to a compound annual growth rate of 44.2%. The number of federative units recording at least one procedure increased from five to 16. Despite this nominal diffusion, São Paulo accounted for 69.1% of national production in 2025 and the Southeast for 77.7%. The HHI across federative units was 0.497, equivalent to only 2.01 equally productive units, and the Gini coefficient was 0.893. Nine federative units recorded no outpatient production in any year. The North accounted for 0.7% of procedures in 2025. Establishments outside public administration accounted for 89.1% of that year's recorded production. Conclusions Recorded approved outpatient CXL production in the SUS increased rapidly and was observed in a growing number of federative units, but procedure volume remained heavily concentrated in a small number of states. These findings describe the geographic distribution of recorded outpatient production rather than individual access, service availability, or population need. A more complete assessment will require age-specific population denominators, patient residence, interstate referral flows, hospital records, and establishment-level data.