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 with a new scanning mid-infrared laser system. METHODS: Six adult cats were treated with 6-mm diameter photorefractive keratectomy (PRK) corrections. One eye in each animal was untreated as a control 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 microm with a new scanning delivery system. The pulse width was 7 nanoseconds, the repetition rate was 10 Hz, the size of the laser spot on the eye was 1.0 mm, and the fluence was 150 mJ/cm2. Healing of the cat corneas was followed for 4 months. Slit-lamp and corneal topography evaluations were done 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 topography showed corneal flattening. Light microscopy at 4 months revealed normal epithelium and increased keratocyte density in the anterior third of the cornea. Electron microscopy showed discontinuities in the basement membrane and 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 activity in the anterior stroma was the only noticeable response besides the flattening shown by topography.