Timing of corneal cross-linking in eyes undergoing intracorneal ring segments for keratoconus: same-day versus staged CXL: a systematic review and meta-analysis.

BACKGROUND

In keratoconus managed with intracorneal ring segments (ICRS) plus corneal cross-linking (CXL), ICRS primarily reshapes the cornea while CXL provides biomechanical improvement and shape stabilization. However, clinical practice varies regarding whether CXL should be performed on the same day as ICRS or delayed, and it remains uncertain whether CXL timing modifies the postoperative optical and topographic outcomes of ICRS.

METHODS

We systematically searched PubMed, Web of Science, Scopus, and the Cochrane Library from inception to October 2025 and included seven comparative studies (2010-2025; 2 randomized trials, 5 cohorts) comparing same-day ICRS + CXL versus staged (typically CXL 3-6 months later). Outcomes covered ΔCDVA/ΔUDVA (logMAR), refractive cylinder and spherical equivalent (SE), keratometry (Kmax, K1, K2, Km), and adverse events; Common-effect models summarized pooled effects.

RESULTS

Visual acuity improvements were equivalent between strategies with no heterogeneity (I2 = 0% for both ΔCDVA and ΔUDVA). Refractive changes (cylinder, SE) clustered near null, indicating comparable refractive normalization. Keratometry showed no difference in ΔKmax, while ΔKm trended toward slightly greater flattening with same-day surgery, narrowly missing significance; K1 and K2 showed similar, non-definitive flattening trends favoring simultaneous treatment. Safety was comparable overall; pooled adverse events did not differ meaningfully between strategies.

CONCLUSIONS

Same-day and staged ICRS + CXL provide similar gains in vision and refraction with comparable safety at 6-12 months, addressing short-term outcome differences attributable to CXL timing rather than progression control. Small keratometric signals favoring simultaneous surgery are not conclusive. Either strategy is reasonable; larger, well-designed randomized trials with longer follow-up should test whether subtle keratometric differences translate into superior long-term stability.