PURPOSE. Previous literature on histopathology of keratoconus is infrequent and contains little or no quantifications. This study attempted to enhance our understanding of keratoconus using a morphometric approach.
METHOD. Three human keratoconic corneas were immediately fixed in 2% gluteraldehyde in 80 mM sodium cocadylate buffer following removal. The tissue was processed, embedded, sectioned and stained for light and transmission electron microscopy. Epithelial thickness, areas lacking anterior limiting lamina (ALL), and thickness of the cellular layers surrounding large fluid pockets on a cornea with hydrops were assessed.
RESULTS. The proportion of total corneal area examined lacking ALL was determined for the 3 corneas (73.63%, 45.57%, 11.72 %). Average epithelial thickness with ALL present was 98 um (range: 20-190 um), while with ALL missing it was 120 um (range: 20-190 um). The average number of epithelial layers with ALL present was 7.98 cells (range: 3-19), and with ALL missing, the average number of layers was 8.25 cells (range: 3-15). A high incidence of stromal cells was present in areas lacking the ALL. Epithelial defects such as abnormal cell morphology, profiles and microcystic edema were predominately noted in areas lacking ALL. The cornea with hydrops was observed to have developed a cellular lining around large pockets of fluid. These linings varied in thickness from 10-240 um (av 110 um) and were formed by 2-25 stromal cells (av 9.21).
CONCLUSIONS. Previous literature, on keratoconus, reported focal breaks or holes in the ALL. In contrast, this study showed large areas lacking ALL. The extensive loss of ALL may have allowed further and more extreme steepening of the cornea and appeared to disrupt normal epithelial regeneration and health. The pronounced migration of stromal cells toward areas lacking ALL appeared to correlate with anterior stromal scarring. The layer of stromal cells surrounding the fluid pockets is suggestive of a protective mechanism activated when hydrops occur. Following the absorption of the fluid in these pockets, it is proposed that these cells are the basis of the scarring resulting from hydrops.