Refractive surgery is a well-established field, and today surgeons have a number of available options to choose from when treating patients. From intrastromal correction to surface ablation to lens-based strategies, the aim of these techniques is to provide patients with a better refractive status and, in as many cases as possible, spectacle independence. One of the most common approaches to refractive correction is laser vision correction. In this and the next five articles, a collection of authors provide an overview of the latest laser vision correction platforms and treatments.
The WaveLight EX500 excimer laser (Alcon Laboratories, Inc.) is the latest in a line of very fast flying spot lasers to come from the WaveLight stable. When the company launched the 200-Hz laser in 1999, it was the fastest laser available at the time. Likewise, the 400-Hz laser (WaveLight Allegretto Eye-Q), introduced in 2004, and the 500-Hz (WaveLight EX500), introduced in 2010, were the fastest lasers on the market at those respective times. Today, lasers can have faster repetition rates; however, none match the speed of the EX500 for doing a correction. A myopia treatment at a 6-mm optical zone takes 1.4 seconds per diopter, and at a 6.5-mm optical zone (my default diameter) it takes 1.9 seconds per diopter. However impressive its speed, this is by no means the laser’s overriding feature. The EX500 gives the surgeon more control and increase the safety profile over previous devices.
I have done comparative studies of the refractive outcomes after laser vision correction with the 400 Eye-Q and EX500 laser platforms. Results are quite similar, with the EX500 just shading the Eye-Q laser in most parameters (Figures 1 through 3). Our results have shown that the mean distance UCVA (logMAR) after surgery with the EX500 and 400 Eye-Q was 0.03 ±NAN and -0.02 ±0.13 (P<.0003), respectively; the mean distance BCVA (logMAR) was 0.09 ±NAN and 0.08 ±0.04 (P<.0004), respectively; the mean manifest spherical equivalent was -0.2 ±0.09 and -0.29 ±0.35 (P<.0001), respectively; the mean manifest cylinder was -0.27 ±NAN and -0.32 ±0.2 (P<.0013), respectively; and the mean refractive error was -0.11 ±0.12 and -0.21 ±0.24 (P<.0001), respectively.
The EX500 shares the same ablation profiles as the Eye-Q. The standard ablation profile for both platforms is wavefrontoptimized, which is what we use for 85% of our primary procedures. If customized treatments are required, a decision tree is followed to choose among four ablation profiles:
- Wavefront-guided, based on the Allegretto Wavefront Analyzer data (Tscherning);
- Topography-guided, T-CAT, derived from data from the Placido-disc Topolyzer;
- Topography-guided, Oculink, derived from the Scheimpflug Oculyzer device; and
- Asphericity-guided, using Custom-Q profiles.
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With the EX500, however, the above options have been improved further. The Topolyzer Vario provides more than just topography information, such as pupil information and pupil centroid shift for all pupil sizes measured during the examination. Additionally, data are obtained from the iris and limbus to aid the cyclorotational tracker in actively and passively ensuring that the ablation is delivered to the intended location. The Oculyzer II, also known as the Pentacam HD (Oculus Optikgeräte GmbH), provides more high-definition data than the previous Oculyzer.
The Custom-Q ablation profile is unchanged. The laser software interface was updated to include three places for data entry: (1) using a built-in keyboard on the laser, (2) on the screen attached to the laser using a mouse and pull-down menus, and (3) on the planning laptop. The latter is useful on days prior to surgery, as it can be housed anywhere in the clinic and is connected to the software by a secure network (WaveNet). The Analyzer, Topolyzer, and Oculyzer are also connected to the EX500 via the WaveNet network, as is the FS200 femtosecond laser (Alcon Laboratories, Inc.). This greatly increases efficiency and safety and reduces input errors, as it eliminates multiple input entries on the different devices.
There are multiple other features on the laser platform, but I will discuss only those that I am very familiar with and use on a regular basis:
Online optical pachymetry. This feature increases patient safety, as the surgeon immediately knows the flap thickness and residual corneal thickness prior to starting ablation utilizing a no-touch technique. It is quick and simple to use and correlates with preoperative Pentacam pachymetry and postoperative optical coherence tomography flap thickness measurements.
Heads-up display in the microscope. The right ocular contains patient name, date of birth, the eye to be treated, the ablation profile to be used, the strength of the eye-tracker signal, and the progression of the ablation as a percentage.
Motorized zoom.The microscope is cataract-surgery quality and can be programmed to automatically zoom in or out at different stages of the procedure. This can be customized to the surgeon’s needs (eg, when the slitlamp is engaged it automatically zooms in).
LED slit lamp. This feature is one that I have enjoyed greatly since 2001, and I now cannot imagine doing a LASIK without a slit lamp. I cannot recall the last time a patient was brought back to the laser room to remove interface debris or a particle.
Eye tracker. The new eye tracker will engage six dimensions, namely x and y, passive and active cyclorotation, tilt (eye roll), and dynamic pupil centroid shift. The eye tracker is also motorized, no longer swinging over the patient’s chest but dropping from within the laser bridge over the eye. This is a big improvement and makes treating patients with large chests easier and more comfortable. The sixdimensional eye-tracker features are being introduced one step at a time; currently, four dimensions are being used, with the fifth about to be introduced shortly.
Patient bed. The new bed has motorized head tilt and head position functions. It is key to the smooth use of the laser, especially if it is used in conjunction with the FS200.
Comparison of ablation profiles. To aid in decision making, the ablation profiles that are being considered for a treatment can be compared on the same screen.
Screen. The on-screen information is so comprehensive that the entire procedure can be done by looking only at the screen, if that is the surgeon’s preference. The microscope view and eye-tracker view are side by side. All other data are intuitively placed. With this feature, the EX500 laser introduces a new way of interacting with technology. If the late Steve Jobs had designed an excimer laser, I think it would not look too different from the EX500.
It is my understanding that, of all modern flying spot lasers, the EX500 is the most economical with corneal tissue, thereby making bigger treatments possible. It is interesting to note that when a clinical trial of optical ray-tracing–guided LASIK was completed 1 year ago, this profile saved even more tissue with even better refractive outcomes. Hopefully it will not be too long before the ray-tracing profile is available on all EX500 lasers.
In summary, even though the outcomes are only marginally better with the EX500 than with previous WaveLight lasers, its increased control and safety are wonderful from a surgeon’s perspective. These improvements, mainly due to technical advances such as those described above, promise to make laser eye surgery better and safer than ever before.
- With the EX500, a myopia treatment at a 6-mm optical zone takes 1.4 seconds per diopter; at a 6.5-mm optical zone it takes 1.9 seconds per diopter.
- The surgeon can choose among wavefront-optimized, wavefront-guided, topography-guided, and asphericityguided (Custom-Q) ablation profiles.
- Safety and control have increased thanks to numerous technological advances.
- The laser is economical with corneal tissue.
- The laser has the widest range of treatment possibilities.
- Ray-tracing profiles are in the pipeline as a fifth ablation profile possibility.
Arthur B. Cummings, MB ChB, FCS(SA), MMed (Ophth), FRCS(Edin), practices at the Wellington Eye Clinic & UPMC Beacon Hospital, Dublin, Ireland. Dr. Cummings is an Associate Chief Medical Editor of CRST Europe. He states that he is a consultant to and clinical investigator for Alcon/WaveLight. Dr. Cummings may be reached at tel: +353 1 2930470; fax: +353 1 2935978; e-mail: abc@wellingtoneyeclinic. com.