Excimer laser: flying spots
Latest excimers lasers use a technology called 'flying spots' (sweep by spots): the energy of laser light is distributed in the form of pulses, whose diameter is close to 1 mm. Each spots "ablate" some corneal tissue.
The different ametropia correction (myopia, hypermetropia and) astigmatism) is accomplished by a selective distribution of spots, in order to reproduce the desired ablation profile. The spots are directed on the cornea after reflection on present mirrors within the licensing system. These mirrors are controlled by the licensing of the excimer laser system: they allow to lead each spot on the target, and are slaves to the system of prosecution eye (eye tracker). During the procedure, the patient's eye fixed a focus (ex: flashing green light target). This target may appear as a 'task' more or less extended to the patient, due to the light spread caused by the realization of the flap and the dehydration of the corneal stroma subjected to fire. If the eye moves or jerks during fixation, eye prosecution system modifies the angulation of the mirrors of fire in real time, to compensate for the movement of the eye. The newest lasers are equipped with eye-tracking systems that 1024 images of the eye per second! This is necessary because the firing frequency of the excimer lasers modern reached 500 Hz (500 shots per second!).
The 'flying spots' technology - scanning by spots - allows flexibility for the realization of different "patterns" of sculpture needed to correct optical defects. The correction of hyperopia and astigmatism requires a pattern of relatively 'complex' sculpture, and the realization of large areas of transition.
The following video was made by filming the shots delivered by the EC500 Wavelight laser with a smartphone (iPhone 4S) by 'below'. This laser delivers the spots at the frequency of 500 Hz. This rate is much higher than the current video acquisition, also the video captures only a small proportion of issued fire... The iPhone was fitted with an accessory lens (macro), in order to focus on the target which was to experience a calibration in PMMA plate. Shots were also filmed by the camera of the Wavelight excimer laser, and an overview could be captured through a second smartphone (Samsung Ativ S).