Ryan Alfonso, MPH
Managing Editor
Each excimer laser system has to be taken in the context of the integrated systems with which they’re marketed. For example, at the American Academy of Ophthalmology meeting in New Orleans this past November, AMO had a huge push to rebrand their entire system as “iLasik”. This includes the newly acquired Intralase femtosecond laser, used more recently to create a thin “sub-Bowman’s” flap of approximately 100 microns, combined with the VISX CustomVue with iris registration. Previously this had been branded as the CustomVue system (prior to the addition of Intralase), but clearly caused some confusion with CustomVision and CustomCornea marketed by some physicians using the Alcon LADARvision system. In addition, ALCON’s LADARVision® Excimer Laser System is also not really sold as an individual component since the laser is sold with LADARWave™ Aberrometer. Nidek also has an excimer system, as does WaveLight, Carl Zeiss Meditec and Bausch & Lomb. The WaveLight system (now controlled by Alcon) is increasing in market share and is now on par with LADARvision, but both are still dwarfed by the dominant player, AMO.
Some know that “excimer” is technically a misnomer derived from the words “excited” and “dimer”. A more accurate term, though rarely used, is “exciplex” since it’s really an “excited complex” vs. a dimer. But, few remember that excimer lasers were initially designed by scientists in Moscow in the early ‘70s. The decades that followed brought layers of innovations leading us to some incredible technology. A great example of which is the development of pupil and limbus tracking. This has obviated the worry of decentration by allowing the excimer system to compensate for saccadic movement and tortional relaxation on reclining.
There are certain basic conditions that all laser systems require for proper function. Of great importance is a carefully climate controlled environment, particularly with regard to room humidity. HEPA filtration has also been suggested as it reduces airborne particulates. Another key factor that has been addressed by all systems is the evacuation of the plume of ablated stromal tissue which could potentially obstruct the beam. In all cases, these lasers are computer controlled using proprietary algorithms for the correction of myopic or hyperopic spheres and spherocylinders. In theory, they could all be integrated with a variety of corneal topography systems, wavefront systems, and keratectomy systems. The good news for patients is that 88% of refractive surgeons now use wavefront systems according to a recent ASCRS survey.
Highlighting the advantages of the major systems:
- AMO’s STAR S4 IR™ Excimer Laser System uses Iris Registration for a more precise wavefront map, making it virtually impossible for physicians to operate on the wrong eye or the wrong patient. Also has ActiveTrak 3-D Active Eye Tracking and automatic centering
- WaveLight Allegretto Z – extremely fast laser (newer 400 Hz model) utilizing wavefront optimized ablations.
- Alcon’s LADARvision – Has suffered bad press as a result of the recall of the 6000 system, but the 4000 does have a track record of good results with CustomCornea ablations.
- Bausch & Lomb’s Technolas - Utilizes PlanoScan™ 2000 software for precise scanning spot technology.
Several studies address variability of outcomes with different refractive laser systems. They often try to link some aspect of the overall system to the results. Undoubtedly the laser itself plays a vital part in clinical outcomes. In a paper published in the Journal of Refractive Surgery in July of 2007 (J Cataract Refract Surg. 2007 Jul;33(7):1158-76), authors Binder and Rosenshein compared the Visx Star S4, LADARVision 4000, and WaveLight Allegretto systems in the correction of myopic spheres and spherocylinders using conventional algorithms vs. wavefront-guided treatments. In this retrospective study of 721 eyes, the authors found that each of these systems had their strong suit. Though they all improved uncorrected visual acuity and best spectacle-corrected visual acuity, wavefront significantly improved outcomes with the Star 4, but not quite as important with the LADARvision. It is important to note that in Allegretto’s study, wavefront-guided did not prove any benefit over wavefront-optimized ablations. Michael Gordon, MD recently spoke at cornea subspecialty day of the AAO stating that custom profiles only outperformed optimized ablations when pre-op RMS was > 0.3 which includes only 20% or so of the general population. Another study from late last year showed that Alcon’s CustomCornea LADARVision4000 system induces fewer higher order aberrations than the WaveLight Allegretto system (Tran DB, Shah V: J Refract Surg. 2006 Nov;22(9):S961-4.).
What explains these differences? Though conceptually “a laser is a laser”, the long and short of it is that different laser platforms achieve different outcomes depending on refractive, patient, and surgical variables. This means the surgeon really has to master their system of choice, know its limitations, and continually refine their treatments.