Investigation on collagen re-structuring during corneal laser welding by a multimodal microscopy approach

Laser welding of corneal tissue is a technique used to provide immediate closure of corneal wounds. The procedure lies in the staining of the cut with a solution of Indocyanine Green followed by continuous wave irradiation with an 810 nm diode laser at low power densities (12-16 W/cm2) which induces a local heating in the 55-65 °C range. In this study we present a multimodal microscopy approach aimed at evaluating the structural modifications induced in the stromal collagen of porcine eyes upon diode laser welding. After laser irradiation the lamellar arrangement was lost and a densely packing of collagen bundles increasingly disordered appeared at the weld site. The persistence of collagen second-harmonic generation (SHG) signal (as detected by SHG microscopy) as well as the fully preserved ultrastructural properties of collagen fibrils at this site (as detected by electron microscopy) pointed out the avoidance of collagen denaturation. These results suggested the occurrence of some structural modification to certain interfibrillar noncollagenous components as proteoglycans responsible for stabilizing and maintaining the orderly arrangement of fibrils within the corneal stroma.