TThe unique Centurion SES microkeratome (CIBA Vision, Duluth, GA) produces standard LASIK flaps but will also offer surgeons an epikeratome with which to create an epithelial flap by means of mechanical subepithelial separation. The microkeratome is currently 510(k) approved in the US for LASIK, and CIBA Vision hopes to offer the epikeratome for subepithelial separations later this year.
AN UNUSUAL DESIGN
Unlike other microkeratome systems, the Centurion SES uses a bar design for applanating the cornea that compresses only the portion of the cornea directly adjacent to the blade's cutting edge. The company states that this feature creates a smoother-edged corneal flap for LASIK that may heal more rapidly. For ease of use, the blade and cartridge are combined in a single unit in order to provide excellent visibility during flap creation (Figure 1). The Centurion SES is designed for nasally hinged flaps.
Mechanism
Perhaps the most intriguing aspect of the Centurion SES is the epikeratome that CIBA Vision plans to introduce later this year. The device can perform automated mechanical separations of the epithelium by substituting a disposable, oscillating PMMA block for the usual blade of the microkeratome. This bladeless separation of the epithelium, dubbed Epi-LASIK by the device's developer, Ioannis Pallikaris, MD, of Crete, Greece, may give rise to a new procedure that features the safety of surface ablation and some of the benefits of LASIK, including rapid visual recovery and minimal postoperative discomfort for patients.
Whereas LASEK uses alcohol to loosen the epithelium and create a cleavage plane within the epithelial basement membrane, Epi-LASIK strives to create a cleavage plane beneath the epithelial basement while avoiding the toxicity of alcohol. CIBA Vision proposes that the flap of epithelium and its intact, underlying basement membrane will rapidly heal, thereby promoting quick visual recovery. In the unlikely event of a poor-quality epithelial flap, the surgeon simply discards the flap and converts the procedure to a standard PRK.
Safety
I have had the opportunity to use the EpiEdge epikeratome for subepithelial separations in animal eyes, and I found it quite easy to perform the separations consistently. Regarding safety, I created a number of subepithelial separations in porcine eyes. Several times, I replaced the device over the reflected epithelial flap, activated it, and made a second pass over the exposed stromal bed. I found it reassuring that the oscillating PMMA block would not engage or cut the underlying stroma. In fact, the stromal tissue appeared completely undamaged.
Results
Preliminary results from patients treated in Crete by Dr. Pallikaris' group with Epi-LASIK using the Centurion SES and EpiEdge epikeratome have demonstrated good postoperative comfort and rapid visual recovery. In a conversation with Dr. Pallikaris (April 2003), he stated that these patients have not developed the corneal haze associated with surface ablation, and the postoperative discomfort they have experienced has been comparable to that associated with LASIK. The amount of myopia treated is low to moderate (-2.00 to -6.00 D).
CONCLUSION
Although experienced refractive surgeons have a low incidence of flap-related complications, these problems constitute a large percentage of all refractive surgical complications. As a result, many surgeons will find the possibility of eliminating or significantly reducing flap-related problems exciting. If this procedure lives up to its promise, it will represent a major technological advance. Numerous patients who have thin corneas would benefit from surface ablation with rapid visual recovery and a minimal risk of haze. Patients and surgeons alike, meanwhile, would be attracted to the bladeless appeal of this technology. Further study of the technology is merited.
Many surgeons abandoned LASEK after concluding that the procedure was no better than PRK in terms of visual recovery, patient discomfort, and postoperative corneal haze. Will these mechanically separated epithelial flaps be truly viable or simply a devitalized scaffolding for a new sheet of epithelium to cover the induced defect? When the Centurion SES epikeratome becomes more widely available later this year, we may learn the answer to this question.
Steven J. Dell, MD, is Director of Refractive and Corneal Surgery at Texan Eye Care in Austin, Texas. He holds no financial interest in the technologies or company described herein. Dr. Dell may be reached at (512) 327-7000; sdell@austin.rr.com.
