Healing after photorefractive keratectomy in cat eyes with a scanning mid-infrared Nd : YAG pumped optical parametric oscillator laser

PURPOSE: To evaluate the healing characteristics of cat corneas treated wit h a new scanning midinfrared laser system. METHODS: Six adult cats were treated with 6-mm diameter photorefractive ker atectomy (PRK) corrections. One eye in each animal was untreated as a contr ol and the other was treated with either a -3.00 or -6.00 diopter ablation. The laser was a new Nd:YAG pumped optical parametric oscillator laser at 2 .94 mu m with a new scanning delivery system. The pulse width was nanosecon ds, the repetition rate was 10 Hz, the size of the laser spot on the eye wa s 1.0 mm, and the fluence was 150 mJ/cm(2). Healing of the cat corneas was followed for 4 months. Slit-lamp and corneal topography evaluations were do ne at each follow-up examination. Histology was performed at the end of the study. RESULTS: The corneal epithelium healed within 1 week. There was no stromal haze in any eye after the epithelium healed. After the first 2 weeks, slit- lamp examination could not identify which eye was treated. Corneal topograp hy showed corneal flattening. Light microscopy at 4 months revealed normal epithelium and increased keratocyte density in the anterior third of the co rnea. Electron microscopy showed discontinuities in the basement membrane a nd hemidesmosomes. The deep stroma and endothelium were normal. CONCLUSIONS: Cat corneas treated with the new optical parametric oscillator laser healed normally with no adverse effects. Increased keratocyte activi ty in the anterior stroma was the only noticeable response besides the flat tening shown by topography.