MMP9 and Schnyder corneal dystrophy: The immunohistochemistry results showed that there was no positive expression of VCAM1 or MMP-9 in the control group, but VCAM1 expression was found in vascular endothelial cells and subendothelial foam cells in both the CHD and SCD groups, while MMP-9 was mainly expressed in the cytoplasm of inflammatory cells in the shoulder area and bottom of the lesion, as indicated by yellow or brown staining of some nuclei (Fig. 4C).