HISTOLOGIC-CHANGES AND WOUND-HEALING RESPONSE FOLLOWING 10-PULSE NONCONTACT HOLMIUM - YAG LASER THERMAL KERATOPLASTY

BACKGROUND: Noncontact holnium:YAG laser thermal keratoplasty (I-Io:YA G LTK) is a promising new technology for correction of hyperopia and a stigmatism. We studied the acute histologic changes and wound healing response following Ho:YAG LTK performed with treatment parameters enco mpassing those used in clinical studies. METHODS: We performed 10-puls e noncontact Ho:YAG LTK on three human corneas 1 day before their remo val at penetrating keratoplasty and on six New Zealand white rabbit co rneas followed for up to 3 months. Tissues were studied with light and transmission electron microscopy and immunohistochemistry. RESULTS: T he amount of acute tissue injury increased according to the pulse radi ant energy. In human corneas, changes in the irradiated zones included epithelial cell injury and death, loss of fine filamentous structure in Bowman's layer, disruption of stromal lamellae, and keratocyte inju ry and death. In the rabbit corneas, similar acute changes were noted. By 3 weeks, epithelial hyperplasia and stromal contraction were prese nt. Wound healing in the rabbits included repair of the epithelial att achment complex, keratocyte activation, synthesis of type I collagen, partial restoration of stromal keratan sulfate and type VI collagen, a nd retrocorneal membrane formation. CONCLUSIONS: Noncontact Ho:YAG LTK produces acute epithelial and stromal tissue changes and in rabbit co rneas stimulates a brisk wound healing response.