Corneal collagen cross-linking combined with simulation of femtosecond laser-assisted refractive lens extraction: an ex vivo biomechanical effect evaluation.

Abstract

To evaluate biomechanical changes induced by in situ corneal cross-linking (CXL) with stromal pocket delivered enhanced concentration riboflavin and high-fluence, high-energy UV-A irradiation. Eight human donor corneas were subjected to intrastromal lamellar corneal tissue removal of anterior 140-μm deep, 80-μm thick × 5-mm diameter central stromal buttons, extracted through a 3.5-mm width tunnel, surfacing in the superior cornea periphery. Enhanced concentration riboflavin solution (0.25%) was instilled in the pocket. In study group A (CXL), superficial high-fluence UV-A irradiation was applied, whereas in control group B (no CXL), none. To comparatively assess changes in corneal rigidity, corneal specimens were subjected to transverse biaxial resistance measurements by application of a unidirectional tangential shear force. Biomechanical differences were evaluated through stress and Young shear modulus. Stress at 10% strain was 305 ± 24 kPa in study group A versus 157 ± 11 kPa in control group B (relative difference Δ = 107%, P = 0.021). Stress at 20% strain was 1284 ± 34 kPa in study group A versus 874 ± 29 kPa in control group B (Δ = 47%, P = 0.043). Average shear modulus in study group A at 10% strain was 6.98 ± 1.12 MPa versus 4.04 ± 0.85 MPa in control group B (Δ = 73%, P = 0.036). Average shear modulus in study group A at 20% strain was 11.46 ± 0.75 MPa versus 8.80 ± 0.72 MPa in group B (Δ = 30%, P = 0.047). Adjunct CXL in this ex vivo simulation refractive lens extraction procedure seems to provide significant increase in corneal rigidity, up to +107%. These findings also support our previous reported work on laser in situ keratomileusis combined with CXL.