An excimer laser (Allegretto Wave Eye-Q, Alcon Laboratories) offers a number of unique features that collectively contribute to outstanding outcomes when using this platform to perform LASIK for a wide range of refractive errors, according to Dr William Culbertson.

The excimer laser can be used to treat spherical equivalent errors ranging from –14 to +5 D, and surgeons have the option of using a wavefront-optimized ablation profile (Wavefront Optimized) or performing a wavefront-guided treatment (A-CAT) using data from a diagnostic device (Allegro Analyzer, Alcon Laboratories).

The excimer laser was installed in late 2008 at the Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, USA. The efficacy, safety and predictability results being achieved are impressive, said Dr Culbertson, holder of the Lou Higgins Distinguished Chair in Ophthalmology and professor at the Bascom Palmer Eye Institute.

At the Institute, a cut-off of >0.4 µm higher-order aberration RMS is used to select eyes for the customized treatment, so 95% of cases are being performed with the wavefront-optimized technique. Considering patients with myopia among the first 250 eyes treated, 100% of eyes were within 0.5 D of the targeted spherical equivalent, 92% were seeing 20/20 or better uncorrected and 99% achieved 20/30 or better uncorrected visual acuity.

Overall, during the course of the year, only a single enhancement procedure was performed (<1%), whereas prior to acquiring the laser, all patients were told that they faced a 5% chance of needing a second procedure, he said.

Figure 1: Post-myopic LASIK (3 months) (Range –1.10 to –11D spherical equivalent). Ophthalmology Times/Source: William W. Culbertson, MD.

In addition, problems with glare and halos at night are reduced relative to experience with other excimer laser platforms, especially considering eyes receiving higher corrections. Dr Culbertson attributed the latter safety benefit to the wavefront-optimized ablation profile that assures a prolate cornea.

Two other excimer lasers are in use at the institute (VISX STAR S4 IR, Abbott Medical Optics; MEL 80, Carl Zeiss Meditec).

"With the aim of providing patients with the best outcomes, each case is reviewed individually to determine if there are specific characteristics that would support using a particular laser," he said. "Based primarily on the outstanding outcomes being achieved with the [newly installed laser system], we now are using it for the majority of our LASIK procedures."

Hardware, software features

High speed is one of the key characteristics of the platform. The laser has a repetition rate of 400 Hz and a spot size of 0.95 µm. Treatment times to correct 1 D of myopia and 1 D of hyperopia are 2.5 and 5 seconds, respectively. Corresponding treatment times using another laser (VISX STAR S4 IR) are 8 seconds and 20 seconds, respectively, Dr Culbertson said.

"The high speed reduces treatment time and remarkably so for hyperopic corrections," he said. "There is a reduced likelihood for the development of corneal drying or loss of patient fixation during the ablation period, events that can compromise ablation accuracy."

The flying-spot scanning pattern of the newly installed laser helps to avoid fluid buildup that can lead to central islands during treatment of high myopia. For hyperopic treatments, the platform offers the benefit of ablating a large, 6.5-mm optical zone with a blend zone to 9 mm.

Other features of the laser include high calibration accuracy and precise fluence delivery. In addition, the laser is well-designed ergonomically in terms of open access to the eye, which is helpful both to the surgeon and for minimizing claustrophobic feelings for the patient.

The fixation light is obvious to the patient and thereby aids in fixation ability. Other features include microscope optics and a scanning slit-lamp attachment that allow the platform to be used to perform a variety of minor corneal procedures.

Dr Culbertson noted, however, that the platform is not perfect. It ablates more tissue for a given dioptric correction than other lasers, and it would not be the laser of choice in eyes where it is important to minimize ablation depth. In addition, corrections with the laser can be made only in 0.25-D increments, and the platform lacks iris registration technology. Therefore, it is important to mark the vertical and horizontal axis carefully prior to starting the laser when treating eyes with >1 D of astigmatism.

Phototherapeutic excimer laser keratectomy is not possible with the laser and Dr Culbertson said he uses another laser (VISX STAR S4 IR) for that purpose.

"However, considering the incredible outcomes, the benefits of the machine seem to trump any of its drawbacks," he concluded.