In 2010, our practice acquired an Amaris 750S laser (Schwind eye-tech-solutions). The technical parameters of the laser, and the willingness of the support team to listen and adapt to our needs, were outstanding. The Gemini Eye Clinic is a high-volume facility; therefore, the speed and reliability of online data transfer between our electronic medical record (EMR) system, diagnostic workstation, and laser are of tremendous importance. Today, with our EMR system connected to the Schwind Scout diagnostic workstation and the Amaris laser, our patient turnover has increased.
The default set-up regarding diagnostic data is to use filtered higher-order aberrations (HOAs) to perform aberration- free treatment with an optical zone of 6.5 mm for myopia or 6.75 mm for hyperopia. We change this default set-up whenever we need to adapt the profile due to pupil size or aberrations. Most procedures are all-laser LASIK, with flap creation performed using the Femto LDV Crystal Line femtosecond laser (Ziemer Group).
ABLATION
There is no need to move the patient between flap creation and excimer laser ablation. The ablation speed is very high, as the Amaris 750S uses a dual-fluence concept. Approximately the first 80% of the ablation is performed with higher pulse energy, and the last 20% is completed with lower pulse energy to achieve the smoothest possible ablation surface using a small spot size of only 0.54 mm and a super-Gaussian beam profile. The percentage distribution varies depending on the kind of treatment and the amount of refractive error to be corrected.
It is important to protect the cornea from cumulative overheating generated by the laser pulses. Schwind’s Intelligent Thermal Effect Control prevents damage to the surrounding corneal tissue because the laser pulses are distributed in a thermally optimized, dynamically adapted way, giving each position on the cornea sufficient time to cool down before being hit by another laser pulse.
EYE TRACKER
The Amaris 750S has a 1,050-Hz eye tracker with a reaction time of the eye-tracker camera of 1.6 ms. The more perfectly the eye is centered and the laser spots are positioned, the more precise the results of the refractive treatment will be. Thus, the Schwind Amaris laser system continuously tracks and actively compensates complex eye movements in six dimensions: the x, y, and z axes, the horizontal and vertical rolling movements of the eye, and cyclotorsion, the eye’s rotation around its optical axis. Advanced Cyclotorsion Control compensates for both static cyclotorsion, the torsional difference between the upright and supine positions (Figure 1), and dynamic cyclotorsion, the rotating movement of the eye during the laser treatment.
The eye tracker simultaneously detects the pupil and the limbus, the size of which remains constant unlike the pupil diameter. The limbus is used as a secondary reference for ablation, so that the center of the ablation is maintained throughout the treatment. Automatic monitoring of pupil size during static cyclotorsional control ensures additional safety. Illumination is automatically adjusted so that the pupil size at the beginning of treatment matches the size at the preoperative examination.
ONLINE PACHYMETRY
The Schwind Amaris 750S also features noncontact online pachymetry, which provides information about corneal thickness throughout the treatment and eliminates the need to touch the cornea with the ultrasound pachymetry probe. The pachymetry values are displayed on the treatment screen (Figure 2). Measurements are taken before the preparation and after lifting the flap, calculating the flap thickness during and after the laser treatment. All data are documented in the treatment log.
WORKFLOW
The straightforward workflow with the Amaris 750S starts with a check-up in the morning. If a new gas filling is needed, it is done via a fully automatic process that takes about 5 minutes. Calibration of the Amaris laser is performed by assistants in about 3 minutes. Evaluation of the result is carried out automatically. Treatments with the Amaris laser systems can be performed for up to 2 hours after a fluence test before the next fluence test is required.
SOFTWARE
The Schwind planning software, accessible via both the touchscreen (Figure 3) and keyboard, includes modules to treat presbyopia and to perform therapeutic treatments such as pachymetry-assisted laser keratectomy. The ORK-CAM is an intelligent planning tool for refractive laser treatments such as LASIK. Whether an aberration- free or customized treatment is chosen, aspheric ablation profiles are used, minimizing the induction of aberrations.
ABERRATION-FREE APPROACH
Most of my patients who want to get rid of their spectacles have a good BCVA and no complaints about visual dysfunction. For most of these patients, I use an aspheric aberration-free ablation (Figure 4). This provides excellent results without having to consider individual wavefront data. Spherical or cylindrical refractive values are exclusively corrected. It is important that the aberration-free ablation should not induce any HOAs during the treatment.
The aberration-free approach is based upon the hypothesis that it is not always advantageous to preoperatively remove existing HOAs (minor native aberrations). Studies with untreated eyes have shown that patients with above-average visual acuity can also have some HOAs.1 Because the brain, with the help of neural compensation, adapts to aberrations, patients have less need to adapt to a new visual situation if we leave their original HOAs, provided that these do not cause clinically significant problems.2-4 The reliable nomogram also takes into account the patient’s age. The results are precise and reliable with a low rate of fine tunings.
CUSTOMIZED TREATMENTS
HOAs that impair vision should be corrected. In this case, we use Schwind’s wavefront-guided customized treatment (Figure 5). Ocular wavefront treatments have the advantage of being based on objective refraction of the complete human eye system, whereas corneal wavefront treatments have the advantage of independence from accommodation effects or lightpupil interactions. Corneal wavefront is also advantageous in treating corneas that have previously undergone refractive surgery. When evaluating the potential outcomes of wavefront customization strategies, wavefront aberration analysis (both total and corneal) is useful to determine whether the goals of the customization can be achieved. In most customized treatments we compensate for lower-order aberrations and corneal HOAs only.
READY FOR SURGERY
Amaris procedures are standardized and softwareguided. The same workflow is used for all treatments. It starts with the import of the planned treatment file. If necessary, all of the parameters can be modified directly at the excimer laser. After the data are imported, there is the possibility to rotationally adjust the laser profile by comparing eye landmarks on the patient lying underneath the Amaris laser with the diagnostic data from the upright measurement. For customized treatments and whenever astigmatism is greater than 1.00 D, I compensate for possible cyclorotation. Retrospectively seen in most patients, cyclotorsion is not significant, but when it occurs, compensation is helpful to achieve the intended outcome. Next, the debris removal system, which stops automatically about 4 cm above the eye, creates constant laminar airflow.5
The eye tracker automatically locks in, and the treatment starts with the push of the footpedal. The dynamic cyclotorsion tracking always compensates for rotational movements during the treatment, independent of whether static cyclotorsion was compensated for or not. I never have to worry because at the beginning of the treatment, before the first pulse, the reference image is taken and the laser device automatically compensates for eye movements in all six dimensions.
CONCLUSION
Our experience with the Amaris 750S laser resulted in the purchase of four systems for several Gemini Eye Clinics in the Czech Republic. So far the lasers are reliable with a low maintenance cost. Earlier this year, we also obtained a free software upgrade. Later this year, we plan to couple our Amaris lasers with a nanosecond laser from Schwind for LASIK flap creation.
TAKE-HOME MESSAGE
- The 1,050-Hz eye tracker continuously tracks and actively compensates complex eye movements in six dimensions.
- Noncontact online pachymetry eliminates the need to touch the cornea with the ultrasound pachymetry probe.
- Whether an aberration-free or customized treatment is chosen, aspheric ablation profiles are used, minimizing the induction of aberrations.
Pavel Stodulka, MD, PhD, is Chief Executive Officer of the Gemini Eye Clinic, Czech Republic. Professor Stodulka states that he has no financial interest in the companies or products mentioned. He may be reached at fax: +420 577 216 900; e-mail: stodulka@lasik.cz.
- Villegas EA,Alcón E,Artal P.Optical quality of the eye in subjects with normal and excellent visual acuity.Invest Ophthalmol Vis Sci.2008;49(10):4688-4696.
- Chen L,Artal P,Gutierrez D,Williams DR.Neural compensation for the best aberration correction.J Vis. 2007;7(10):9.1-9.
- Artal P,Chen L,Fernández EJ,Singer B,Manzanera S,Williams DR.Neural compensation for the eye’s optical aberrations. J Vis.2004;4(4):281-287.
