Evaluation Of Corneal Stromal Demarcation Line Depth After Two Different Uv Energies In Corneal Collagen Cross-Linking: A Comparative As-Oct And In Vivo Confocal Microscopy Study

To compare corneal stromal demarcation line (DL) depth following corneal collagen cross-linking (CXL) using two different ultraviolet (UV) energy levels and to evaluate the consistency of in vivo confocal microscopy (IVCM) versus anterior segment optical coherence tomography (AS-OCT).

A single-center, retrospective study conducted at the Laser Myopia Treatment Center of Xi’an No.1 Hospital, China, from June to December 2024.

A total of 28 patients (45 eyes) undergoing epithelium-off CXL were divided into two groups based on UV energy dose:

• Group A (standard fluence): 14 eyes with progressive keratoconus treated with 30 mW/cm² for 4 minutes (total energy 7.2 J/cm²).
• Group B (low fluence): 31 eyes undergoing FS-LASIK XTRA, treated with 30 mW/cm² for 1 minute (total energy 1.8 J/cm²).

All eyes were examined 3 months postoperatively by IVCM (IVCM III RCM, Heidelberg, Germany) and AS-OCT (RTVue100, Carl Zeiss Meditec, Germany). The DL depth was measured using each device’s built-in caliper/analysis software. Statistical analysis was performed using SPSS v26.0 (IBM), with p < 0.05 considered significant.

Both groups showed visible DL by IVCM at 3 months; under AS-OCT, 86% of Group A and 65% of Group B presented a discernible line (p = 0.178). DL depth was significantly deeper in Group A than in Group B by both IVCM and AS-OCT (p < 0.05). In Group A, IVCM (385.00 ± 101.7 µm) and AS-OCT (357.17 ± 92.3 µm) measurements did not differ significantly (p = 0.136). In Group B, IVCM (203.65 ± 73.7 µm) measurements were significantly shallower than AS-OCT (302.25 ± 30.8 µm; p < 0.001).

Reduced UV energy correlates with a shallower corneal DL post-CXL. While both AS-OCT and IVCM can visualize the DL, IVCM may provide a more accurate functional assessment of the cross-linking effect, especially with low-fluence protocols.