Although the skill and experience of the surgeon are the most significant factors affecting the outcome of your LASIK procedure, the surgeon's choice of LASIK system is also important. When the Allegretto Wave Eye-Q system became available, Dr. Winthrop immediately upgraded his LASIK suite to offer his patients the additional safety and efficacy this system provides.
The newest and most sophisticated lasers used in LASIK surgery incorporate what is called a "scanning spot beam" which is free to move about on the surface of the cornea. This allows surface areas to cool and relax before any subsequent pulses come into that area. "Scanning slits" and "broad-beam lasers" (designed to treat flat surfaces) are less dynamic and may subject the cornea to hot spots.
The laser beam profile should be of the Gaussian type as that will treat the curved surface of the cornea more precisely. Top-hat beams were designed to etch flat surfaces like micro chips and their effectiveness in the periphery of the cornea is compromised.
The size of the laser beam has much to do with the quality of vision and also helps to provide accuracy and quality to the resulting vision. A beam of less than or equal to one millimeter is considered appropriate.
The rep (repetitive) rate for any given laser, the same as the hertz (Hz) rate, is the number of laser pulses per second. Medical lasers fire off pulses of energy rather than an uninterrupted stream. The higher the frequency, the better, as the surgery will be that much quicker. This, in turn, means less anxiety for the patient and less drying of the cornea. A drier cornea can over absorb the energy and may result in overcorrection. The Alcon Wavelight Allegretto is the world's fastest laser in the treatment of eyes for myopia, hyperopic and/or astigmatism.
This is the amount of energy over a given area. More is better.
This is how many times/second the tracker on the laser system can detect eye movement. The normal human eye actually moves 20–60 times/second as it scans for information. Thus, any number over 65 is considered good. Patients are asked to remain looking at a target during their procedure; in reality, they are scanning all around the target and occasionally on the target. (Again a quicker surgery will mean less fatigue and a smaller area of scanning).
More important than how many times the machine is noticing eye movement from the patient is just how many times per second the laser system can realign itself to the center of the patient's eye so that the treatment can be directed to the proper place on the cornea. Most systems have good detection rates, but fall critically short in the correction department as a number greater than 65 is required here also. Only the Alcon Ladarvision and the Alcon Wavelight Allegretto are fast enough to place the laser pulses in the exact spot intended before the patient moves again.
Below is a chart highlighting the technical differences between currently available LASIK systems.
|Type of Laser||Scanning
|0.75||1-2||2x9||0.65 – 6.5||0.95||0.7|
|60||100||100||10 – 20||400||200|
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Seiler T. Koller T. In: Albert & Jakobiec's Principles and Practices in Ophthalmology. 3rd ed. Philadelphia, PA: Saunders WB Co; 2008:981-985