Corneal Thickness Measurements Using Time-domain Anterior Segment OCT, Ultrasound, and Scheimpflug Tomographer Pachymetry Before and After Corneal Cross-linking for Keratoconus

PURPOSE: To compare minimum corneal pachymetry assessment using three measurement methods in eyes before and after corneal collagen cross-linking (CXL) for keratoconus. METHODS: Fifty patients ( 54 eyes) who underwent CXL for keratoconus were evaluated with the Visante (Carl Zeiss Meditec), Pentacam ( Oculus Optikgerate GmbH), and ultrasound pachymetry (USP) (Optikon Pacline) to assess corneal thickness at baseline and 1, 3, 6, and 12 months after treatment. RESULTS: Using USP, mean thickness was 456 mu m at baseline, decreased by approximately 8 mu m at 1 month, and then recovered to initial values. The mean difference between Visante and USP was statistically significant, but not clinically significant, and was similar at baseline and after CXL (-1 to -2 mu m, P < .05 except for 12 months). Pentacam had similar readings at baseline (-2 mu m vs USP), but lower corneal thickness after CXL (-12 to -20 mu m throughout follow-up, P < .001). The width of the Bland-Altman 95% agreement interval of Visante and Pentacam with USP was approximately 5 mu m and 15 mu m, respectively. CONCLUSIONS: Visante pachymetry shows better agreement with USP compared to Pentacam after CXL, which may be due to the inhomogeneous reflectivity of the postoperative cross-linked cornea and possibly altered refractive index and acoustic impedance that may influence the observed differences among techniques. [J Refract Surg. 2012;28(8):562-566.] doi: 10.3928/1081597X-20120703-02