Pupil tracking is a crucial component of all modern vision-correcting lasers. This is absolutely necessary to ensure that the treatment is rendered to the exact intended position on the cornea. All laser pulses must be placed with precise knowledge of their position relative to other spots, and relative to the tissue being sculpted. In addition, even if we try to hold our eyes absolutely still (as is encouraged during treatment, for example), the eyes will move slightly due to our heartbeat, breathing, and microscopic visual tracking movements (called fast saccades) of the eyes.
The Allegretto laser can only treat at its rapid pulse frequency if it also has an ultra-fast eye tracking system to follow eye movement during treatment. This laser incorporates an infra-red pupil tracking system that determines the exact pupil position with a sampling frequency faster than the treatment or pulse emission frequency. Every 5 milliseconds, the eye’s location is measured and the internal mirrors of the Allegretto are automatically aligned. Right before the pulse is released, a second check is made to confirm that the eye has not moved. This happens 200 times every second, once for every laser pulse.
If, at any time, the eye moves too quickly to be measured or moves out of range, the laser will stop and wait for the eye to move back into position. This ensures that each of the “perfect pulse” spots is placed in the “perfect position” on the treated surface of the eye. Should the eye ever move too fast or out of range of the tracking system during treatment, the laser will automatically pause the treatment, and wait until the eye is back in position. The combination of direct surgeon observation and high-speed pupil tracking ensures that treatment will be rendered “on target” every time, with each pulse. The animation at left above shows how the tracker functions to guide each laser pulse to the exact intended point on the cornea.
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