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 Optikgeräte 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 μm at baseline, decreased by approximately 8 μm 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 μm, P<.05 except for 12 months). Pentacam had similar readings at baseline (-2 μm vs USP), but lower corneal thickness after CXL (-12 to -20 μm throughout follow-up, P<.001). The width of the Bland-Altman 95% agreement interval of Visante and Pentacam with USP was approximately 5 μm and 15 μm, 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.