Preliminary in vitro study of the histological effects of low fluence 193-nm excimer laser irradiation of corneal tissue

PURPOSE: To determine if moderate numbers of low fluence, 193-nm excimer la ser pulses modify or damage the corneal stroma. METHODS: The corneal epithelium of fresh bovine eyes was scraped off and th e exposed stroma was irradiated with 200 low fluence laser pulses from an a rgon fluoride excimer laser. This process was performed on five eyes each a t two laser fluences, 10 mJ/cm(2) and 30 mJ/cm(2). The ten irradiated and t hree control (unirradiated) corneas were sectioned and studied by electron microscopy. The maximum and minimum thickness of the anterior layer of rand omly oriented collagen fibers was measured using electron microscopy. RESULTS: The mean maximum thickness of the anterior randomly oriented layer of collagen was 1.23 +/- 0.45 mum in the control corneas, 0.67 +/- 0.32 mu m in the corneas irradiated at 10 mJ/cm(2), and 0.10 +/- 0.12 mum in the co rneas irradiated at 30 mJ/cm(2). The mean thickness of corneal stroma remov ed was 0.7 mum at a fluence of 10 mJ/cm(2) and 1.1 mum at a fluence of 30 m J/cm(2). A thin, electron-dense pseudomembrane was present at both fluences . CONCLUSION: We report removal of bovine corneal stroma at 10 mJ/cm(2)-below the previously reported ablation threshold of 20 mJ/cm(2).