Why will refractive surgeons want to incorporate customized ablation into their practices? The answer is the same as why they began performing LASIK when they were already successful with PRK. Our first customized results already outshine those we have achieved with PlanoScan (Bausch & Lomb Surgical, San Dimas, CA), which are the best results ever approved by the FDA, and I believe that our outcomes can only improve.

I have worked with both LADARVision (Alcon Laboratories, Inc., Fort Worth, TX) and the Zyoptix system (Bausch & Lomb Surgical). They are both outstanding units with many advantages over earlier technology. My choice today, however, is the Zyoptix system, quite simply because it delivers the best results with this procedure. Zyoptix is planned as a full system, treating myopia, hyperopia, and astigmatism. In several international locations, we have also begun using the system to treat eyes that have had previous surgery, for which we have achieved good results.

FULL DIAGNOSTIC INFORMATION
The Zywave wavefront sensor is a Shack-Hartmann type of wavefront aberrometer. It is linked in a single unit—a dual-head workstation—with the Orbscan IIz corneal topographer. This combination provides the surgeon with a unique blend of information. With the patient seated one time at the workstation, this diagnostic system measures his aberrations, corneal surface and shape, pachymetry, pupil size, and both his posterior and anterior float. Combining the Zywave and Orbscan data on a single screen enables the surgeon to preview the ablation profile overlaid on the corneal thickness for the entire cornea and the amount of tissue to be removed. This ability heightens procedural safety.

The system takes multiple readings, automatically selects the best, and then generates a floppy disk that transfers the information to the T217z scanning excimer laser. The surgeon can control the size of the optical zone in any degree up to an inner zone of 7 mm and an outer zone of 10 mm and, if he wishes, may adjust the amount of myopia or hyperopia to be treated beyond the computer's recommendation.

Compared with LADARVision, the Zyoptix system has fewer centroids, which are the focal points of the individual lenslets of the aberrometer that each measures portions of the optical system. There are advantages and disadvantages to each approach. The Zyoptix system condenses more information into each centroid, so the centroids have more spacing from each other. I believe that the system is therefore less prone to crossover. More centroids, while containing the same amount of information, split it up into smaller packets. There is a diminishing return as the number of centroids increase, as well as the aforementioned crossover error. The best compromise number is debatable, as these approaches show. The real answer lies in the results, as I will demonstrate.

TRACKING
The Zyoptix system features a video-based, infrared eye tracker that I have found to be very precise. The important factor to consider when evaluating eye trackers is their response time. This measure tells how much time elapses between when the tracker takes a reading and when it can direct the laser pulse accordingly. The response times of the Zyoptix system and the LADARVision platform are within 10% of each other, depending on whom you consult. This equivalence, which affects the number of laser pulses applied to the eye and how many times the laser beam is directed, is more important than how frequently the eye is measured.

The Zyoptix system features a more user-friendly eye tracker than does LADARVision. Dilating the pupil is unnecessary, and it is permissible to wipe the cornea during the laser treatment. Neither system offers rotational tracking, but both will allow the surgeon to set a guide such as limbal markings as a means of discerning cyclotorsion. Again, the real answer lies in the results.

THE LASER
The T217z is a scanning-spot, 50-Hz laser that offers both a 1- and 2-mm spot size. It features a shaping lens that creates a truncated Gaussian-beam profile. This shape increases the beam's efficiency at tissue removal. Treatment commences with 2-mm spots and progresses to 1-mm spots, all laid down in the pattern dictated by the diagnostic system. The system allows registration of the x-, y-, and z-axes, as well as of cyclotorsion.

The customized results with the Zyoptix system beat the PlanoScan results (the best ever documented in the FDA trials of approved excimer laser platforms) and compare very favorably with those for LADARVision.1 Of the Zyoptix eyes, 91.5% were 20/20 without correction, compared with 79.9% of the LADARVision eyes. Importantly, the Zyoptix results included all eyes (sphere and cylinder), while Alcon reported on only spherical eyes.

In the FDA trial data, another important metric is the efficacy ratio, which is the percentage of patients whose postoperative UCVA was better than their preoperative BCVA. This number closely reflects the average patient's reason for undergoing LASIK surgery: to see as well without glasses as he ever did with them. Alcon's FDA results showed that 52.5% of patients reached this goal. These were the spherical myopes only, without astigmatism. By contrast, 78.3% of Bausch & Lomb's group reached this important goal, and the group included all eyes, sphere and cylinder patients.

Wavefront ablation is purportedly safer than traditional LASIK. This assertion is best evaluated in eyes that gained best-corrected vision. In the Alcon group, 37% of eyes gained lines of BCVA after surgery, an excellent result. The Zyoptix cohort, however, was even more impressive, with 60.4% of eyes gaining BCVA. The Zyoptix system also reduced the amount of induced aberrations, with a higher percentage of patients showing less third- and fourth-order aberration postoperatively than preoperatively, as compared with the Alcon system.

Finally, an advantage of Zyoptix is surgeon's extensive experience worldwide with the system. In the past 2 years, over 100 systems have been used to treat tens of thousands of patients.

COMFORT
I have used and am certified on all the major laser systems. I think that the T217z is the easiest excimer laser to use, and I find the Zyoptix system to be exceptionally satisfying ergonomically. The system has a perfect working distance and offers superior magnification, along with excellent depth of field. With its wide range of magnifications, the microscope is very adjustable, as befits a surgical workstation. The bed is stable and moves quickly. I also appreciate the lack of a post in the middle and the fact that the eye tracker automatically finds and tracks the eye. There are no extra steps, unless the surgeon does not want the tracker to engage, in which case he must perform an additional keystroke. Also, I appreciate that the Zyoptix system does not distort the z-axis—a problem with LADARVision.

Bausch & Lomb offers a complete LASIK system; they produce the laser, aberrometer, topographer, and keratome. I do not need to mix and match products. Finally, the Zyoptix system is an excellent workstation. I have repositioned IOLs and actually performed a penetrating keratoplasty beneath its microscope.

PATIENT SATISFACTION
The best way to illustrate how happy my patients have been with customized ablation using the Zyoptix system is to describe the results of a 45-patient study in which I participated.¹ Subjects had one eye randomized to standard LASIK using the standard, approved PlanoScan software and the other to customized ablation using the Zyoptix system. Patients and observers were masked regarding treatment. The results were better in the Zyoptix eyes. More telling, however, is that patients with 20/20 UCVA OU preferred the visual quality of the eye treated using Zyoptix. In the patient survey results for the entire Zyoptix cohort, the system was unsurpassed, with 98% of patients satisfied and none dissatisfied.

Stephen G. Slade, MD, FACS, is in private practice in Houston. He is a consultant for Bausch & Lomb Surgical. Dr. Slade may be reached at (713) 626-5544; sgs@visiontexas.com.

1. US Food and Drug Administration, Center for Devices and Radiological Health. LASIK eye surgery: FDA-approved lasers for LASIK. Available at: http://www.fda.gov/cdrh/lasik/lasers.htm. Accessed January 2, 2003.