Introducing Allegretto Wave
Allegretto Wave
This portion of our website discusses in some detail the often technical reasons InSight Lasik chooses Allegretto’s laser vision-correction systems in our clinic. The staff at Insight Lasik encourages patients to be well-informed and educated with their options, and this segment of our website shares some of the more technical information about the laser and vision-correction technology and process. We hope to provide this information in a way that is thorough but accessible, so that each of our patients will feel comfortable and confident in whatever decision they make about their personal vision-correction options.
The Allegretto laser is the fastest and most precise laser system for vision-correction available in the United States today. When accepted in 2003 as the first new laser in five years to be FDA approved in the U.S., the Allegretto Wave merited the widest approval range ever initially granted to a new laser for both myopic and hyperopic vision-correction.
The Allegretto Wave is manufactured by Wavelight, a company based in Erlangen, Germany. Wavelight’s aim is to integrate the best of outstanding German engineering with proven optical design to produce vision-correcting lasers with unparalleled precision and accuracy. With its PerfectPulseTechnology™ that safely and accurately controls each pulse of energy emitted from the laser from start to finish, and its unique ability to holistically evaluate and retain the cornea’s natural curvature, the Allegretto testifies to a laser vision-correction system designed for performance, safety, and comfort.
An Overview
Some of the features that help differentiate and distinguish the Allegretto laser from the competition include:
• An exceptionally stable laser engine, creating extremely stable performance over typical laser treatment time intervals;
• Exactingly precise calibration;
• The only laser system to address the "cosine correction offset" problem;
• The only laser to take into account the starting curvature radius of the cornea being treated, with the intent to preserve the naturally aspheric ("prolate") corneal shape after treatment;
Clinical data presented to FDA showed that quality of night vision after treatment was better than night vision quality before treatment, with either glasses or contact lenses
Wavefront Optimization and Optical Zones
The Allegretto Wave is able to produce some of the largest available optical zones, or treatment zones. A larger optical zone is crucial for patients with very large pupils, and enhances the correction procedure for higher order aberrations like halos, poor night vision, and glare. If a patient’s pupil is larger than the optical zone, the patient is at risk for poor peripheral vision and other higher order aberrations. In the past, this has been one of the biggest drawbacks to traditional laser surgery. The Wavefront Optimization available with the Allegretto laser confronts this limitation.
At night and in low lighting, the pupil becomes larger to permit the maximum amount of light to enter the eye. Laser eye correction needs to take the pupil’s expansion into consideration, because if the optical zone is smaller than the size of the pupil at its largest, there is a good chance that the patient will experience poor night vision or problems with glare and halos around bright objects such as oncoming headlights. ALLEGRETTO WAVE® is able to produce not only a larger optical zone, but a blend zone. This blend zone applies individually calibrated algorithms in a peripheral treatment around the optical zone. It also preserves the cornea’s initial curvature radius, recreating the original, naturally curved surface of the eye, virtually eliminating glare and night vision problems associated with older generation lasers.
Click here to read more about Allegretto’s Wavefront Optimization technology (link to Wavefront Optimization page (row 6 in the spreadsheet)).
Precision
The Allegretto system was designed later than other lasers, including the Visx, LADAR, and Technolas lasers. Because of this, its engineers have learned from and avoided the imperfections and shortcomings in previous laser systems. Rather than “upgrading” or “patching” the laser system as new technology and research surfaced, the Allegretto system was able to incorporate advanced optical treatment methods (like the Wavefront Optimization discussed above) from the outset.
Lasers that correct vision do so by sculpting a shape change in the cornea. In a nearsighted eye, correction with glasses or contacts requires addition of a concave lens in front of the eye (the eyeglass, or contact lens). Laser treatment works instead by sculpting to subtract a convex lens-shape from the cornea. Each laser pulse creates a tiny, sub-microscopic "bite" in the eye so that, in aggregate the entire treatment (all the pulses together) sculpt exactly the intended shape change. The more precisely each "bite" can be, the more precise the excised shape can be, and the better the precision of the final result. Optical physicists discuss laser effects in terms of beam shape, beam diameter, and energy density or fluence. Consistency of beam characteristics is crucial to reproducibility of results. A Schematic of the Allegretto beam profile is shown below.
On several levels, the Allegretto laser has a better performance record than other laser systems for vision-correction. The main laser is extremely stable over extended time intervals (hours and days) relative to the intervals employed in treatment (seconds). The laser beam is among the most exact and consistent produced by any laser system, so the "bites" of each pulse are uniform. The laser beam shaping system also has the fewest moving parts of any laser system, reinforcing consistency and reliability. The beam-shaping section of the laser is specifically maximizes the performance of each optical component, including lenses and mirrors, used to shape and aim the beam (using a sealed beam chamber and Nitrogen gas 'washout' after treatment).
Speed
Although treatment time varies depending on the laser system used and the number of diopters to be corrected, the Allegretto operates at a pulse rate of 200 pulses per second, more than twice that of other “scanning spot” systems. Because the eye is living tissue, it is important that treatment proceed quickly. The collagen layer of the cornea is the part sculpted in LASIK, and it contains some water. In LASIK, a superficial flap is created, then pulled back from the treatment area, and remains open for the duration of laser treatment. During even the short intervals involved in modern laser treatment, the longer the flap remains open, the more water can evaporate from the exposed tissue. This is referred to as stromal dehydration. Relatively dehydrated stroma will have a slightly greater collagen fiber density (less water between the fibers), so laser pulses will remove slightly more collagen tissue per pulse than in normally hydrated tissue. These effects are small, but not insignificant. The faster the laser treatment can be rendered, the less stromal dehydration can (adversely) affect the desired result. This is yet another reason why InSight Lasik operates with the Allegretto laser system.
Safety
One of the most common questions potential-patients ask (in the context of laser vision correction) is, "How can I know that the treatment will be safe, and will go the way we want?" There are essentially three components to address in this regard:
1. Risks related to creation of the LASIK flap;
2. Safety of the laser treatment itself; and
3. Post-operative considerations (stability of correction or need for enhancement).
We will evaluate the laser treatment itself, as the first and third issues are evaluated in the pages linked below.
All lasers approved for use in the United States for vision-correction by the FDA must demonstrate numerous safety features. These include, but are not limited to the following:
• Providing electrical power reserve in case of a power outage (they all have backup power systems)
• Providing a means to accurately calibrate and measure energy at the point of treatment
• A design of built-in safeguards that will suspend treatment if necessary, should there be any malfunction detected within the laser, with the ability to resume treatment from exactly where it was paused
• Systems must exist to suspend treatment if the eye tracker should fail to maintain fixation on the eye being treated, with methods in place to confirm fixation and resume treatment thereafter
• Extensive documentation of operation, service and maintenance.
The Wavelight Allegretto laser system received US FDA approval in October, 2003.