M.D. Toolkit

Defining SOA Vision Correction

The iLASIK platform yields stability and smoother operations.

By Stephen C. Coleman, M.D.

More than 20 years ago, refractive surgery became a reality, offering ophthalmologists a new skill set with which to improve quality of vision for their patients. Since the approval of photorefractive keratectomy (PRK) in 1996, 15 million eyes have been treated worldwide, with yearly volumes reaching 1 million in the United States alone. Substantial refinements in accuracy, predictability, and customization have been made during this time, evolving a nascent technology into what it is today.

In order to fully appreciate the strides made in laser vision correction (LVC), it is important to remember its predecessor, radial keratotomy (RK). Primarily a Russian technique, this early form of refractive surgery was exported to the rest of the world 24 years ago and became the state-of-the-art vision correction of its day. Shortly thereafter, however, studies regarding the excimer laser began to emerge, and the first patient was treated by Marguerite McDonald, M.D., using a VISX 20/20A prototype.

Today we have at our disposal iLASIK (Advanced Medical Optics), which combines Advanced CustomVue with IntraLase to create a far more sophisticated procedure. This technology builds on the forerunners of refractive surgery by taking advantage of the best features of both PRK and conventional LASIK.

Similar to PRK, iLASIK offers minimal disturbance of the anterior stroma, thereby increasing corneal stability. Wavefront-guided excimer treatments produce rapid visual recovery without haze, an outcome also seen with conventional LASIK. But the IntraLase component notably permits precise control of flap architecture, a feature that reduces the risk of ectasia by allowing the surgeon to consistently create a very thin, anterior, sub-Bowman's flap.

In my practice, I only offer patients iLASIK. Having performed refractive surgery starting with first generation PRK, I believe that this technology offers patients and surgeons alike the outcomes initially envisioned with this procedure. Enhancement rates have dropped to 3% in my practice since I incorporated iLASIK technology, and have the potential to decrease even further. What gives me the most confidence in this approach though, is the fact that I can rely on a very tight standard deviation for a desired target depth; the resulting flap is consistently thin, just below Bowman's membrane, which maximizes residual corneal strength.

The WaveScan system captures the unique imperfections in patients' eyes, which enhances CustomVue outcomes.

The STAR S4 IR is the excimer laser component of the iLASIK system.

Improving Outcomes

With each successive advance in laser technology, visual outcomes have steadily and significantly improved. Utilizing standard deviations around a desired endpoint as a measuring tool, I have found that these parameters have become considerably tighter since the debut of PRK, indicating a move toward more reproducible results.

Two primary advances have largely contributed to this improved predictability of visual outcomes possible today: FDA approval of LASIK in 1999 as well as FDA approval of wavefront-guided, customized ablations for LASIK in 2003. Proper labeling assisted doctors when discussing LASIK with prospective patients and served as the foundation upon which the entire LVC market grew. Three years later, I was fortunate to be involved with the initial clinical studies for wavefront-guided ablations. Completed in 2003, this clinical trial led to full FDA approval in that same year. Now, wavefront-guided ablations comprise 55% of all LVC procedures, of which 62% are performed using the iLASIK platform, according to the Market Scope "2007 Annual Refractive Surgery Report."

Just because something is new, however, does not necessarily mean it is better. Is state-of-the-art laser technology truly measurable then, and does it improve outcomes? The excimer laser has improved in many ways over the years since the VISX Star made its debut in 1996, first with the approval of LASIK, and later with the addition of improved surface smoothness due to variable spot scanning (VSS), 3-dimensional eye tracking and wavefront-guided custom ablations to name a few.

Standard deviations have narrowed with each of these advances, but arguably the most significant improvement was the change from Zernike to Fourier analysis when describing a patient's wavefront. The most recent addition, iris registration (IR), has further shifted the standard deviation favorably. Similarly, the adoption of the ultrafast femtosecond laser (IntraLase) over bladed microkeratomes has been shown to decrease outcome variability. (Figure 1)

The latest generation of femtosecond and excimer laser technologies have made Advanced CustomVue possible and have contributed significantly to the groundbreaking announcement by one of refractive surgery's most high-profile clients: NASA. After analyzing visual stability and accuracy data from LVC patients, NASA approved use of all LASIK with Advanced CustomVue and IntraLase for its astronauts. This is roundly regarded as a historical step forward for LVC, a strong validation of its merits, and speaks volumes when discussing the advantages of wavefront-guided LASIK when compared to conventional LASIK.

Figure 1. The variability of outcomes, as shown above, decreased with the adoption of the femtosecond laser.

The most persuasive argument for iLASIK for me, and undoubtedly for NASA, is its ability to consistently create stable, customized flaps with a femtosecond laser. Refractive surgeons desire a more anterior flap, where the collagen is most densely packed, to ensure a stable eye postoperatively and lower the risk of ectasia as well. A comparison of an 80 μm flap to a 140 μm flap has demonstrated a loss of corneal strength of only 14%, vs. 25% with the thicker flap. And growing research shows that flap position, which is highly controllable when using an IntraLase, also plays a critical role in preserving corneal integrity.

I still perform conventional procedures in my practice, but only in those unique circumstances where I am unable to capture wavefront data from a patient's eye. This typically occurs only in a setting where a patient has sustained previous trauma, has a corneal scar or has undergone prior RK. Otherwise, I only offer my patients the most progressive laser technology that will give them the excellent outcomes they expect. It's an added bonus that I am able to reassure patients that their surgery is approved for military aviators and astronauts. If iLASIK is suitable for those flying a multi-million dollar aircraft, then it follows that it's likely also ideal for people who drive their cars on the highway at night. From a surgeon's perspective, the birth of iLASIK has resulted in greater stability, fewer enhancements and happier patients. OM