Outcomes of the Sub400 Protocol and Contact Lens-Assisted Corneal Cross-Linking in Advanced Thin-Cornea Keratoconus: Clinical Efficacy and Long-Term Visual Stability.

PURPOSE: To compare the clinical outcomes of the sub400 protocol and contact lens-assisted corneal cross-linking (CACXL) in patients with keratoconus with corneal thickness below 400 μm.

METHODS

This retrospective study included 88 eyes of 88 patients with progressive keratoconus and thinnest pachymetry <400 μm. Group 1 (n = 50) underwent sub400 CXL using individualized fluence at 3 mW/cm2, whereas group 2 (n = 38) received CACXL with 10 mW/cm2 for 9 minutes after functional pachymetry was increased above 400 μm using a riboflavin-soaked contact lens. Outcomes at 12 months included corrected distance visual acuity, keratometric parameters, thinnest corneal thickness, demarcation line (DL) depth, endothelial cell density, and progression rate.

RESULTS

Twelve months after surgery, tomographic stability was maintained in 45 of 50 eyes (90%) in the sub400 CXL group and in 33 of 38 eyes (86.8%) in the CACXL group. No eyes in both groups showed signs of endothelial decompensation. DL depth was significantly greater in the CACXL group (296.32 ± 43.22 μm) than in the sub400 group (266.44 ± 48.63 μm; P = 0.002), with a negative correlation between baseline Kmax and DL depth (ρ = -0.226, P = 0.034). No significant changes were observed in Kmax, Kmean, or postoperative thinnest corneal thickness in both groups (P > 0.05).

CONCLUSIONS

Sub400 and CACXL provide similar short-term efficacy and endothelial safety in thin corneas. CACXL achieves deeper stromal penetration, although without superior 12-month visual or topographic outcomes. Longer-term studies are needed to determine whether greater DL depth yields sustained biomechanical or refractive benefits.