Characterizing the morphologic changes in collagen crosslinked-treated corneas by Fourier transform-second harmonic generation imaging.

To evaluate the efficacy of using forward second harmonic generation (SHG) and 2-dimensional fast Fourier-transform (2D-FFT) analysis for the label-free characterization and quantification of morphologic changes in the corneal stroma after collagen crosslinking (CXL).Department of Physics, National Taiwan University, Taipei, Taiwan.Experimental study.En face forward SHG imaging and 2D-FFT analysis were performed on ex vivo porcine corneas at the depths of 100, 200, 400, and 800 μm. Morphologic changes in stromal collagen fiber in control, ultraviolet-A (UVA), riboflavin, and riboflavin-UVA treated porcine corneas were assessed. Hematoxylin-eosin staining and Sirius red staining were performed for comparison.Corneas after CXL treatment tended to have collagen fibers that were wavy compared with the linear pattern in normal corneas. Quantitative 2D-FFT analysis of forward SHG images also showed an increase in the standard deviations of the distribution of stromal collagen fiber orientations, which is indicative of the changed pattern of crosslinked stromal collagen fibers.Second harmonic generation imaging showed the morphologic changes in stromal collagen after CXL treatment. The linear collagen fibers in normal corneal stroma became wavy after treatment. With the introduction of 2D-FFT analysis, the morphologic changes can be quantified.