Multipoint assessment of demarcation line depth after standard and accelerated cross-linking in central and inferior keratoconus.

Purpose: To determine the changes in the depth of the demarcation line in the central to peripheral cornea following accelerated compared to standard corneal cross-linking (CXL).

Methods: In this prospective, non-randomized study, 60 eyes with progressive keratoconus underwent accelerated or standard CXL (30 in each group). Anterior segment optical coherence tomography (AS-OCT) was done one month later by two independent masked examiners to measure the depth of the demarcation line in the central cornea and on peripheral rings.

Results: The inter-examiner agreement (intra-class correlation coefficient) was >0.75 for all measured points, and average measurements were used in the analysis. The depth of the visualized demarcation line in the center was 223.4 ± 67.4 μm and 354.9 ± 79.0 μm in the accelerated and standard groups, respectively ( < 0.001). The depth significantly decreased from the center to the 7 mm ring in both groups (all  < 0.05). This change was 7.7-26.1% and 2.2%-11.1% in the accelerated and standard groups, respectively. In the accelerated group, the demarcation line was deeper in the central cone sub-group compared to the inferior cone sub-group, but in the standard group, the demarcation line was deeper in the inferior cone sub-group (all  < 0.05). Cases with an inferior cone showed greater inter-group differences in all studied points.

Conclusions: The depth of the demarcation line with accelerated CXL is less than the standard protocol and decreases from the center towards the periphery. Demarcation lines are more homogenized with standard CXL. In cases with an inferior cone, demarcation line depth varies throughout the cornea.