Pupil Eye Tracker

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 precisely relative to other spots, and relative to the tissue being sculpted. Even if we try to hold our eyes absolutely still (as is encouraged during treatment), the eyes will move slightly due to our pulse, breathing, and microscopic visual tracking movements (called saccadic movement) of the eyes.

The Allegretto laser can only treat at its rapid frequency if it also has an ultra-fast eye tracking system to follow eye movement. This laser incorporates an infrared pupil tracking system with a sampling frequency faster than the treatment frequency. Every 4-6 milliseconds, the eye’s location is measured and the internal mirrors of the Allegretto are automatically aligned. Just before each pulse is released, a confirmatory check is made to ensure 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 eye. The combination of direct surgeon observation and high-speed pupil tracking ensures that treatment will be on target every time, with each pulse.

PerfectPulse Technology

PerfectPulseTechnology™ represents a new approach to laser vision correction - it accounts for speed, precision, and safety in the Allegretto laser, and offers revolutionary improvements over other laser systems. Engineering of the Allegretto laser has taken special steps to ensure that the amount of energy in each pulse of the laser has been calibrated to exactly the right level. After the beam has been created, it passes through three checkpoints on its way through the system. At each of these points, the energy level is checked and adjusted if necessary, ensuring that the beam is perfectly tuned at its destination. The Allegretto laser employs a proprietary overlapping spot placement method to ensure accurate energy placement, and is one of the ways that it achieves a smoother, rounder, and more natural corneal surface than many other excimer lasers.

Wavefront Optimization

One of the most innovative features of the Allegretto is the way it incorporates wavefront optimization to render proper treatment. It is the only laser system that takes into account the starting curvature of the cornea being treated. The Allegretto is the only laser treatment that preserves normal curvature characteristics - thereby optimizing visual quality - as a consequence of treatment.

In earlier laser systems treating nearsightedness, the optical zone, or area of correction, was centered on the cornea; this resulted in a flattened area that ended with an abrupt edge, causing unwanted side effects like poor night vision, glare, and halos. Laser treatment patterns then evolved to apply peripheral laser pulses in a blend zone, to smooth this abrupt edge. All prior laser systems were designed to be calibrated on flat plastic test surfaces. However, the cornea is curved, and when treating on the downslope of this curve, some laser energy is scattered rather than being fully absorbed. This effect - called the cosine offset effect - requires additional pulses to the periphery of the cornea, in order to compensate for the energy lost through scattering and reflection.

The Allegretto system is the only laser platform that applies extra pulses to the peripheral cornea in order to compensate for the angle of the laser beam. The laser anticipates and corrects for any cosine offset issues. The treatment is specifically designed to preserve the naturally aspheric shape of the cornea to a degree that older lasers simply could not achieve. This compensation, combined with the precision of “PerfectPulse” technology (enhancing the accuracy of tissue sculpting with the precision of laser pulses), produces a smooth, cleanly sculpted optical surface—just what is necessary for high performance vision.