Illumination: A Key Element for any Laser Platform

I had the opportunity to use the first Zyoptix 100 excimer laser (Z100; Bausch & Lomb, Rochester, NY) installed in Spain. I formerly used the 217 Technolas and the 217 Z excimer lasers (Bausch & Lomb). I have also worked with the Mel 80 Excimer Laser (Carl Zeiss, Oberkochen, Germany) and the Ladar 4000 (Alcon Laboratories, Fort Worth, Texas). Although each platform was excellent for laser refractive surgery, I chose the Z100 when I bought a new unit. I will point out the main features of the laser that influenced my decision, its changes in comparison to the older version and some comments on possible improvements.

Main Features
Illumination. This is a fundamental and crucial laser component, however, it is rarely mentioned. During my first general surgery class at the Universitat Central de Barcelone, Facultad de Medicina Hospital Clinic, the professor started the lesson by saying that proper preparation of the surgical field and maintenance of the best and clearest view were among the most important pearls of surgery. All surgeons check these things during every surgery.

How many problems have you seen or experienced in a live surgery demonstration or in the surgical theater due to an inappropriate observance of the elementary and fundamental rules listed above? The Z100 is equipped with a new illumination system (Figure 1) that provides an excellent view of the surgical area. The use of cold light, based on white light-emitting diode (LED) technology, is comfortable for the patient; can easily adjust in a wider range of brightness by maintaining constant light color; and does not bother the patient who can see the fixation red light during the procedure. The system provides a better contrast of the image — additionally enhanced by one high-power white LED — integrated at the gooseneck infrared light used in the eye tracker. This provides a flat angle illumination, distinguishing the limits between dark irises and the pupil (resulting in better treatment centration). The microscope has also been upgraded by using Zeiss technology.

Treatment time. The time it takes for laser treatment is another important aspect of laser technology. The Z100 laser source has doubled its repetition rate (from 50 Hz to 100 Hz) and decreased its treatment time by two and a half times. Although each surgical procedure, and especially each patient, deserves individual dedication, it is generally recognized that faster laser treatments improve clinical results; stromal dehydration and a lack of patient collaboration are avoided. Patients undergoing refractive surgery prefer faster procedures.

Registration. One of the most determinant aspects of modern laser platforms is registration — the perfect match between diagnostic information and laser treatment. Registration is important for personalized or customized treatments, based on wavefront data, topography or both. For this purpose, the Z100 platform includes the iris recognition eye tracker, which finds the limbus ring as a reference. Pupil center is calculated relative to this reference (25 µm resolution), determining the pupil center shift between the dilated (examination) and undilated (treatment) pupil. Automatic patient identification is obtained by generation of a digital iris key exported with diagnostic information. Additionally, precise information about scotopic pupils — acquired by integrated active pupillometry — can be used to properly calculate optical treatment zones.

Changes in the z coordinate (z tracking) can also be determined by triangulation through integration of a second camera for iris recognition. The iris recognition eye tracker improves safety and efficacy in refractive procedures. When using more personalized treatments, I find such an eye-tracker system is mandatory for excellent results. My colleagues and I conducted a small study on myopic astigmatism treatments (cylinder >3.00 D). We believe that matching registration is of major importance, and we found a significant improvement in results when using the iris recognition system. Although iris recognition may not be easy to use (there is a learning curve), we always recommend it for personalized treatments.

Planification. As surgeons, we collect data, think and plan, and then proceed with the surgery. The Z100 excimer laser system uses the Zyoptix Treatment Planner (Bausch & Lomb) to provide ablation algorithms, optimizing pulse distribution and saving tissue. All treatments benefit from a combination of 2-mm plus 1-mm spots and truncated Gaussian beam shape, giving a wider range of treatment options. There are three main objectives when combining options: leave residual stroma about 300 µm; adjust the optical zone to the scotopic pupil with a 0.5 mm maximum difference; and use wavefront-guided tretaments when higher-order aberrations are >0.3 µm (root mean square for 6-mm pupil).
Improvements to Come
What about an even more perfect laser? Some things are already coming, such as control of torsional eye movements during treatment (through a new torsional eye-tracker dynamic system) and intraoperative pachymetry control (using optical coherence tomography [OCT] technology). We are convinced that these devices will improve our clinical results.

Additional Wants for a Laser
During a refractive procedure, I would like to check laser data directly though the microscope. If laser information was directly displayed into the microscope lenses, I would not have to alternatively look at the laser screen to find this information. Have you seen The Terminator (or other robots in science-fiction movies) checking images and data at the same time?

Tilting the laser source to follow the tilt movements of the eye is another improvement I would like to see. The laser beam would always maintain its perpendicularity in relation to the eye, resulting in less energy loss, more efficient precise treatment and perhaps less ablation. Furthermore, OCT technology should be updated. The analysis of preoperative, postablation and postoperative data should permit a better control of our clinical results. In case of enhancements, the system could automatically design a new ablation profile or meniscus based on these data to obtain the perfect shape and result.

Wavefront, topography and Q factor (asphericity) should be integrated to work on personalized treatments for each particular eye. The system should be flexible enough to offer different treatment options based on preoperative data. The Treatment Planner is now a prototype system to be developed. Information should always be displayed in an easy-to-use way.

I may sound too critical, but I am convinced that femtosecond technology is the intermediate step to pure intrastromal ablation and the end of the flap era. We are just tasting what this technology can do for us and for our patients.

The teamwork of engineers, hardware and software experts and surgeons, in combination with our analysis of clinical results, makes the possibility of the perfect laser obtainable. Meanwhile, I congratulate Cataract & Refractive Surgery Today Europe for compiling our thoughts about the possibility of the perfect laser.

Francesc Duch, MD, is from the Institute Catala de Cirugia Refractiva, in Barcelona, Spain. Dr. Duch discloses that he has no financial interest in the products and/or companies mentioned. He may be reached at duch@icrcat.com or +34 93 418 99 29.