Corneal stromal ablation with femtosecond ultraviolet pulses in rabbits

PURPOSE: To determine the effectiveness of femtosecond ultraviolet (UV) pulses in ablating corneal stroma in a rabbit model and to compare the healing response between eyes treated with femtosecond UV pulses and eyes treated with standard excimer photorefractive keratectomy. SETTING: Laser Research Center, Vilnius University, Vilnius, Lithuania. DESIGN: Experimental study. METHODS: Myopic photoablation using a femtosecond UV solid-state laser system was applied to corneas of pigmented rabbits. Experiments in 16 eyes were performed for optimization of the laser system parameters (fluence, spot size, pulse repetition rate) and calibration of ablation rate. In 7 rabbits, deep femtosecond UV ablation (similar to 130 mu m) in 1 eye and shallow ablation (similar to 30 mu m) in the contralateral eye were performed. Nine rabbits received an approximately 30 mu m ablation with femtosecond UV pulses in 1 eye and with a conventional excimer system in the contralateral eye. Two eyes were used as controls. The ablation process and surface-temperature dynamics were monitored and recorded. Surface quality and haze development were evaluated. Rabbits were humanely killed 0 to 6 months after surgery, and eyes were enucleated for histological examination. RESULTS: Rabbit corneas ablated with femtosecond UV pulses or excimer laser radiation were similar in terms of the corneal wound-healing process, surface quality, and histology. CONCLUSIONS: The experiments indicate the feasibility of clinical application of femtosecond UV lasers for stromal ablation. The ability to switch between laser harmonics allows fast changeover from infrared to the UV mode, implying that a wide range of ophthalmic procedures can be performed using a single solid-state laser device.