High-speed recording of thermal load during laser trans-epithelial corneal refractive surgery using a 750 Hz ablation system

PURPOSE: To evaluate the temperature rise of human cornea during trans-epithelial photorefractive keratectomy (trans-PRK) with a 750 Hz excimer laser employing Intelligent Thermal Effect Control (ITEC) software. METHODS: In this observational case series, trans-PRK ablation was performed on 5 eyes of 3 patients using an aspheric profile of a 750 Hz excimer laser system. A high-resolution infrared camera with a frame-rate of 350 images per second was used to determine the corneal surface temperature. Images were taken sequentially, starting a few seconds prior to and ending a few seconds after the ablation. The maximum temperature of any pixel of a given image were recorded and graphed against time. RESULTS: The baseline ocular surface temperature, immediately prior to the beginning of excimer laser, ranged from 32 to 34.9 °C. The maximum ocular surface temperature until the epithelium was ablated ranged from 35.2 to 39.7 °C. The maximum ocular surface temperature during stromal ablation with high and low fluence laser ranged from 32.9 to 36.5 and from 34.4 to 37.7 °C respectively. CONCLUSION: The ITEC software is effective in controlling the maximum temperature rise during laser ablation in the extremely challenging situation of trans-PRK involving high ablation volumes of almost 6000 nl, potentially improving the outcomes. The ITEC system limited the maximum temperature to 39.7 °C in the epithelium, and 37.7 °C in the stroma. The epithelial temperature was always higher than stromal temperature (regardless of high or low fluence irradiation). Safety limit of 40 °C found in the literature was never reached.