Schwind Amaris Systems
Diego De Ortueta
Thomas Magnago
The SCHWIND AMARIS is a sixth generation excimer laser. It has both a 750 Hz and a 500 Hz version. Among the technical advances are:
An Automatic Fluence Level Adjustment (AFLA). The goal of AFLA is to achieve perfect smoothness with high ablation speed. This has been developed to ensure an ideally balanced ratio between the total number of laser pulses and the energy delivered. The result is that approximately 80% of the laser ablation is performed with a high fluence value, while low fluence is used for the remaining 20%. The ideal smoothing of the surface is achieved by adding low fluence pulses at the end of the treatment.
The SCHWIND AMARIS laser uses a small spot size of 0.54 mm and a Super-Gaussian beam profile. The improved spot overlap matrix is designed to provide a precise reproduction of the calculated ablation volume avoiding vacancies and corneal roughness.
The small spot size allows the laser to perform sophisticated ablation profiles with a high-speed ablation time. This reduces the likelihood of significant stromal bed dehydration during a large correction. The 750-Hz laser system at a 6-mm optical zone corrects 1.0 diopter (D) in 1.5 seconds versus 1.0 D in 2 seconds for the 500-Hz laser system.
The SCHWIND AMARIS laser systems work with an Intelligent Thermal Effect Control (ITEC)1 that reduces the likelihood of damage to surrounding corneal tissue, even at the extremely high ablation speed. The ITEC algorithm ensures that the temperature rise of the cornea is <5° and significantly <40°, which is considered critical for corneal tissue denaturation.
The laser systems have an active tracker to monitor the position of the eye 1,050 times/second with an average latency of about 1.6 ms. The total reaction time of the AMARIS is typically <3 ms. The AMARIS 750S laser system continuously tracks and actively compensates for eye movements including dynamic cyclotorsion (DCC), which is the rotating movement of the eye during the laser treatment. The laser detects both the pupil and the limbus. The limbus is used as a reference for ablation because its diameter is stable, meaning that the original ablation center is maintained throughout the treatment. The point selected as the center of the ablation is the same throughout the treatment because the laser system tracks the pupil in relation to the limbus.
The illumination is automatically adjusted to maintain the pupil diameter at the same size at the beginning of the treatment as it was at the preoperative examination when the diagnostic data were obtained.
Real-time pachymetry provides information about the corneal thickness throughout the entire duration of the treatment. The changes are measured and displayed on the treatment screen. The measurements can be taken before the preparation and after lifting of the flap, as well as during and after the laser treatment. This
ensures that the surgeon knows exactly how much tissue has been ablated at all times and the thickness of the remaining cornea. Real-time pachymetry allows the surgeon to change the surgical plan intraoperatively if the stromal bed is thinner than expected. Pachymetric data can be printed and saved for future reference in the event that retreatment surgery is needed in the future.
The microscope for the SCHWIND AMARIS laser delivers good contrast, true color brilliance, and good depth of focus. The diagnostic slit lamp for flap checking is compactly designed and can be moved around two axes across the entire working area.
With the AMARIS laser systems the laser beam is guided through a completely enclosed beam path in a vacuum. No disturbing elements can impair the quality of the laser beam, and there is no deviation of results to be expected as, for example, could occur with the use of nitrogen (Fig. 9.1).
One of the main differences between the two laser platforms is the speed of ablation, which is described with the model numbers 750S and 500E. The z-tracking is only available for the AMARIS 750S, meaning that the AMARIS 500E works with five dimensions of eye tracking. Also, the 500E has a more compact design without a swivelling laser arm.
▪ Treatment Spectrum
The SCHWIND AMARIS laser systems offer a wide range of applications in refractive and therapeutic corneal surgery with the SCHWIND Custom Ablation Manager (CAM). The software includes modules to treat hyperopia, myopia, and astigmatism. The manifest sphere must be within the range of -15 to +8 D, and the manifest cylinder range must be between -7 and +7 D. The spherical equivalent must be within the range of -9 and +6 D.
 FIGURE 9.1 SCHWIND AMARIS 750S. (Courtesy of SCHWIND.) |
Safety and efficacy data support LASIK treatment in the maximum range of -12 D with up to +6 D of cylinder for myopia and up to +6 D for hyperopia with up to +6 D of astigmatism. For photorefractive keratectomy (PRK), the proven maximum spherical correction is -9 D with up to 6 D of cylinder and a maximum of +6 D with up to +5 D of astigmatic correction. As previously stated, higher corrections are possible, but there are no data to support safety and efficacy. Treatment of presbyopia and therapeutic treatments such as pachymetry-assisted laser keratectomy (PALK) or phototherapeutic keratectomy (PTK) are also possible. Supporting multicenter study results have been published.2,3,4,5,6,7,8
The optimized refractive keratectomy (ORK)-CAM9 is a planning software tool for refractive laser treatments such as LASIK or Femto-LASIK, and for surface ablation such as LASEK, PRK, Epi-LASIK, and also the transepithelial photorefractive keratectomy (TransPRK) (Fig. 9.2).
For each planned refractive treatment, the SCHWIND CAM calculates the size of the optimal transition zone, depending on the refraction, treatment method, and optical zone. This provides standardized treatment for more predictable outcomes.
 FIGURE 9.2 SCHWIND CAM software. (Courtesy of SCHWIND.) |
The optical zone is also the effective optical zone. The optical zone can always be optimized, even if there is limited wavefront information available for a customized treatment, for example, due to small pupils. This optimization is achieved by peripheral aspheric enlargement of the optical zone.
The pulse efficiency of laser ablation depends on the depth of the tissue and the cell structure. A LASIK procedure ablating deeper tissue layers requires different parameters from those needed for a surface treatment. Therefore, the ORK-CAM defines the ablation per pulse, depending on the treatment method. This is one of the reasons why nomogram adjustment is unnecessary.
▪ SCHWIND Diagnostic Technology
OCULAR WAVEFRONT ANALYZER
The Ocular Wavefront Analyzer is a highresolution Hartmann-Shack aberrometer that measures 1,024 points with a resolution of 230 µm. Each eye is measured three times to ensure good repeatability. The ocular wavefront analyzer determines total higher order aberrations (HOAs) and root-mean-square (rms) error. An integrated infrared pupillometer allows the determination of scotopic pupil size and calculation of the mesopic pupil size based on aberrometry. The device also measures accommodation and keratometry (K) and calculates the Seidel refraction. In our experience, the Seidel measurement with a 4-mm pupil is close to the manifest subjective refraction and can be used in place of it. The Seidel refraction incorporates HOAs into the spherocylindrical refractive error and allows one to check the data against the patient’s glasses prescription.
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