Purpose: Corneal wound healing after excimer laser photorefractive keratectomy (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 microscopy to verify morphological changes in human corneas in vivo after PRK.
Methods: Ten corneas of eight patients that had earlier undergone PRK were examined at different postoperative time points (7 days-34 months). One of the PRK patients was examined sequentially three times. Three additional corneas, which had earlier undergone corneal grafting surgery and then were subjected to excimer laser photoastigmatic keratectomy (PARK), were studied as well. Seven healthy untreated corneas served as controls to define the normal morphology of human cornea. A tandem scanning confocal microscope (TSCM) was used to generate real-time images of the corneas on an S-VHS videotape. The images were either digitized and further processed or the individual video frames were 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 perceived. The epithelium appeared normal one month post-PRK. Ongoing activation of the anterior stromal keratocytes along with extracellular scar tissue were detected. We also observed increasing numbers of regenerating subepithelial nerve leashes with somewhat twisted pattern. Highly reflective, presumably activated keratocytes were no longer detected 6-7 months post-PRK. Hypercellularity with scar tissue could still be found up to 30 months post-PRK. Only one cornea examined 34 months post-PRK showed normal keratocyte morphology and recovery of the anterior stroma. However, the morphology of subepithelial nerves was still somewhat abnormal. The two corneal grafts examined 11 or 32 months post-PARK exhibited a normal-appearing epithelium but considerable stromal hypercellularity and extracellular scar deposition. The subepithelial nerves were poorly regenerated in one eye and fairly well detectable in the other. The third graft examined 15 months post-PARK revealed the presence of enlarged surface epithelial cells and dense stromal scarring but no nerves.
Conclusion: TSCM clinically confirms the earlier histological 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 addition the thickness of the stromal scar can be be measured for e.g. planning of phototherapeutic keratectomy.