Minimisation of the thermal load of the ablation in high-speed laser corneal refractive surgery: the 'intelligent thermal effect control' of the AMARIS platform

The purpose of this work was to evaluate the extent that minimisation of the thermal load of the ablation in high-speed laser corneal refractive surgery is possible. To do this, thermal load from ablations onto flat PMMA plates was recorded with an infrared thermal camera and analysed for different flying-spot sorting algorithms (from pure randomised to 36 Hz local frequency) using a 500 Hz laser system with a fluence of 500 mJ/cm(2), and aspheric ablation profiles. Each ablation configuration was repeated three times. Thermal load valid for corneal ablations was modelled based upon the results from ablations onto flat PMMA plates. It was found that the thermal load of ablations onto flat PMMA plates declines steadily when the allowed local frequency decreases or when the diameter of the blocked area increases. With this laser system, a local frequency of 39 Hz dynamically controlled over a diameter of 3.865 mm seems to be optimal for avoiding corneal collagen denaturation with minimum compromise on treatment duration. Peak temperature changes of 48 degrees C in PMMA (16 degrees C equivalent cornea) using pure randomised flying-spot sorting algorithms were reduced to 27 degrees C in PMMA (9 degrees C equivalent cornea) using 36 Hz local frequency over a blocked diameter of 4.25 mm. Average temperature changes of 15 degrees C in PMMA (5 degrees C equivalent cornea) using pure randomised flying-spot sorting algorithms were reduced to 7 degrees C in PMMA (2 degrees C equivalent cornea) using 36 Hz local frequency over a blocked diameter of 4.25 mm. Hence, minimisation of the thermal load of the ablation in high-speed laser corneal refractive surgery seems feasible using 'Intelligent Thermal Effect Control'. Clinical evaluations of human eyes are needed to confirm the preliminary simulated results presented here.