Evidence of Apoptotic Cell Death in Keratoconus

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Abstract
To determine the potential role of apoptosis in the noninflammatory degeneration characteristic of keratoconus. Four normal corneas and 16 keratoconus corneas were obtained as archival specimens. Tissues were examined histopathologically for TUNEL immunoreactivity to detect the presence of DNA fragmentation. Tissues were also subjected to single-stranded DNA (ssDNA) analysis, a more apoptosis-specific stain. Normal corneas exhibited fewer than five TUNEL-positive epithelial cells per section, these being very lightly stained. All 16 keratoconus corneas demonstrated extensive, intense TUNEL staining in at least one layer. Fifteen of 16 exhibited staining in the epithelial layer, 11 of 16 in the stromal layer, and 13 of 16 in the endothelial layer, whereas 10 of 16 keratoconus cases demonstrated TUNEL immunoreactivity in all three layers. The ssDNA stain was also positive and evident in all three layers of the cornea, although to a lesser degree than the TUNEL assay. The noninflammatory nature of keratoconus, coupled with the TUNEL in situ results, suggests apoptosis as a mode of cell death in this degenerative disease.