Keratophakia and keratomileusis: histopathologic, ultrastructural, and experimental studies

We present ultrastructural findings in two cases, one of keratophakia (9 months postoperatively) and one of keratomileusis (1 year, 7 months post-operatively), which best demonstrate the pathologic changes we observed in six cases of cryorefractive surgery. In addition, we studied a rabbit model of keratophakia which appears to exhibit similar features to that of human keratophakia. In the keratomileusis cases, there were marked abnormalities, including deposition of redundant basal lamina, loss of Bowman's membrane and deposition of a 6 nm fibrillar material in areas devoid of Bowman's membrane. In keratophakia lenticule we noted the absence of keratocyte regeneration, abnormal deposition of long-spacing collagen, and the presence of necrotic cellular debris. In experimental keratophakia, little to no evidence of keratocyte regeneration was evident 4 months after surgery. Keratophakia lenticules implanted into actively regenerating corneas induced by freeze injury exhibit only a slight increase in the number of keratocytes migrating into the donor tissue, suggesting that implants lack a primary factor necessary for keratocyte regeneration. Immunofluorescent localization of fibronectin and fibrinogen demonstrated absence of these factors in normal host stroma, implanted lenticules and freeze injured corneal stroma. Actively migrating fibroblasts, however, did react positively for fibronectin, suggesting that these cells synthesize and secrete fibronectin during regeneration. These results do not support a role for soluble fibronectin or fibrinogen in keratocyte repopulation.