REAL-TIME CONFOCAL MICROSCOPIC OBSERVATIONS ON HUMAN CORNEAL NERVES AND WOUND-HEALING AFTER EXCIMER-LASER PHOTOREFRACTIVE KERATECTOMY

Purpose. Corneal wound healing after excimer laser photorefractive ker atectomy (PRK) passes through a series of characteristic stages which have earlier been defined by means of histological, histochemical, and biochemical approaches. We investigated the potential of confocal mic roscopy to verify morphological changes in human corneas in vitro afte r PRK. Methods. Ten corneas of eight patients that had earlier undergo ne PRK were examined at different postoperative time points (7 days-34 months), One of the PRK patients was examined sequentially three time s. Three additional corneas, which had earlier undergone corneal graft ing surgery and then were subjected to excimer laser photoastigmatic k eratectomy (PARK), were studied as well. Seven healthy untreated corne as served as controls to define the normal morphology of human cornea. A tandem scanning confocal microscope (TSCM) was used to generate rea l-time images of the corneas on an S-VHS videotape, The images were ei ther digitized and further processed or the individual video frames we re produced with a video printer. Results. Seven days post-PRK in vivo confocal microscopy revealed the presence of morphologically immature surface epithelial cells. Delicate nerves, activated keratocytes and deposition of extracellular Light-reflecting scar tissue were perceive d. The epithelium appeared normal one month post-PRK. Ongoing activati on of the anterior stromal keratocytes along with extracellular scar t issue were detected. We also observed increasing numbers of regenerati ng subepithelial nerve leashes with somewhat twisted pattern, Highly r eflective, presumably activated keratocytes were no longer detected 6- 7 months post-PRK. Hypercellularity with scar tissue could still be fo und up to 30 months post-PRK. Only one cornea examined 34 months post- PRK showed normal keratocyte morphology and recovery of the anterior s troma. However, the morphology of subepithelial nerves was still somew hat abnormal. The two corneal grafts examined 11 or 32 months post-PAR K exhibited a normal-appearing epithelium but considerable stromal hyp ercellularity and extracellular scar deposition. The subepithelial ner ves were poorly regenerated in one eye and fairly well detectable in t he other. The third graft examined 15 months post-PARK revealed the pr esence of enlarged surface epithelial cells and dense stromal scarring but no nerves, Conclusion. TSCM clinically confirms the earlier histo logical data on healing of excimer laser wounds. It offers a distinct improvement in the assessment of excimer laser-treated corneas, as it enables cellular details and nerves to be perceived in vivo. In additi on the thickness of the stromal scar can be measured for e.g. planning of phototherapeutic keratectomy.