Ultrastructure Study Of Keratoconus And The Evidence Of Apoptotic Cell Death

PURPOSE: To explore specific pathological changes in keratoconus by observing the ultrastructure of keratoconus with light microscopy and transmission electron microscopy,test the evidence of apoptosis in each layer of keratoconus and normal cornea,thus discover the mechanisms of keratoconus.METHODS:5 normal human corneas and 11 keratoconus corneas were cut into paraffinsection and ultrathinsection by routine methods,we observed their changes of every layer by light and electron microscopy.Paraffinsection tissues were examined histopathologically for TUNEL immunoreactivity to detect the presence of DNA fragmentation.RESULTS: The following changes were found under light microscopy in keratoconus:thin epithelium and stroma,local rupture or destruction in basement membranes and Bowman's layer,basal cell swollen,stroma disarrangement,ruptures or folds in the Descemet's membrane and thin endothelium layer.Compared with normal cornea under transmission electron microscopy,keratocyte of keratoconus had smaller nucleus with less hetetochromatin,more and larger mitochondria,increased and enlarged rough endoplasmic reticulm and goigi complex of irregular structure,the apoptosis body was found in some cases and large amount of granular deposits among laminae.3 normal corneas exhibited fewer than five TUNEL-positive epithelial cells which were very lightly stained. In contrast,we observed that more and heavy stained TUNEL-positive cells could be found in 10 keratoconus corneas (at least one layer)among 11 cases. The positive staining cells were seen in the epithelium layer of 10 cases,in the stromal layer of 8 cases and in the endothelium layer of 6 cases.6 cases demonstrated TUNEL staining in all three layers.CONCLUSION: Keratoconus is a noninflammatoy degenerative disease, we suggest apoptosis asa mode of cell death by observing its ultrastructure and TUNEL assay .