Exploring corneal strength: Comparative analysis of big bubble and manual lamellar dissection in deep anterior lamellar keratoplasty

PURPOSE: To compare the long-term visual outcomes and corneal biomechanical properties following deep anterior lamellar keratoplasty (DALK) using either the big bubble (BB) technique or manual lamellar dissection (MLD) in patients with advanced keratoconus. In addition, to evaluate the relationship between residual stromal bed (RSB) thickness and post-operative visual and biomechanical parameters in MLD-DALK eyes, and to assess the reliability of intraocular pressure (IOP) measurements.
METHODS: A total of 78 eyes from patients with keratoconus who underwent DALK (43 BB-DALK, 35 MLD-DALK) and completed 18 months of post-operative follow-up were retrospectively analyzed. Corneal hysteresis (CH), corneal resistance factor (CRF), cornea-compensated IOP (IOPcc), Goldmann correlated IOP (IOPg), and best-corrected visual acuity (BCVA) were assessed. In the MLD group, RSB thickness was measured using anterior segment OCT. Biomechanical assessments were performed using the Ocular Response Analyzer.
RESULTS: At 18 months, CH and CRF were comparable between groups (p>0.05), as were BCVA and other topographic parameters. The mean RSB thickness in the MLD group was 75.8±27.7 μm, with no significant correlation between RSB and visual or biomechanical metrics. In both groups, IOPcc was significantly higher than IOPg (p<0.01), though IOP readings were not correlated with RSB thickness.
CONCLUSION: MLD-DALK offers similar visual acuity and biomechanical outcomes to BB-DALK and is a viable alternative when BB formation fails. Clinicians should consider using measurements IOPcc for accurate post-operative monitoring, as traditional methods may underestimate true IOP in DALK patients.s.

Keywords: Big bubble, corneal hysteresis, deep anterior lamellar keratoplasty, manual lamellar dissection