Wednesday, November 5, 2003
Since LASIK’s clinical introduction in 1989, the corneal flap has been created with a microkeratome blade. Ample documentation identifies this step as the source of most risks and complications associated with the procedure, which can include partial and “buttonholed” flaps, epithelial sloughing, corneal wrinkles and flaps that are too thick. The microkeratome uses a significant level of vacuum to applanate the cornea through a suction ring and hold it tightly as the metal blade slices across to produce a flap. Typically approaching 200 microns in depth, the resulting flap is thicker than ideally necessary to expose underlying tissues. Irreducible blade-produced flap thickness sometimes rules out patients with thin corneas as appropriate surgical candidates. Gradual modifications of surgical technique and improvements in microkeratome manufacture have helped mitigate untoward results, but the insult to corneal tissue introduced by this mechanical process cannot be entirely eliminated.
IntraLase Corp., headquartered in Irvine, CA, now offers ultra-fast laser technology, the IntraLase FS, as a replacement for the microkeratome. Researchers at the University of Michigan’s Kellogg Eye Center and the National Science Foundation’s Center for Ultrafast Optical Science collaborated in pioneering the approach, which yields thinner, more precise corneal flaps than even the most delicate and skillful manual technique. The device has received Food and Drug Administration approval and is rapidly becoming the state-of-practice technique nationwide.
The IntraLase FS technology is distinguished by the speed of the laser pulse — in the femtosecond (one quadrillionth of a second) range. The laser uses a long wavelength (1053 nm) and its accuracy (+/- 10 microns, with a spot size of only three microns) is unparalleled by any other technology in refractive surgery. The IntraLase FS creates a thinner flap than possible using the microkeratome blade (as little as 100 microns) under very low vacuum, delivering the laser energy directly to the stromal layer of the cornea through a disposable glass lens. The outer surface of the cornea suffers no trauma and the procedure is completely painless. The incision produced by the IntraLase FS device has a vertical edge. This difference in flap architecture may reduce the chance of corneal epithelial ingrowth. In testing, greater flap stability as well as a high degree of accuracy in both the depth and size of the resection has also been demonstrated.
The “total laser” procedure, utilizing the IntraLase FS laser and a standard excimer laser, avoids microkeratome-related complications such as corneal irregularities and scarring, and may offer the potential for better vision following LASIK, recognizing that precise control at every surgical step strongly correlates with accuracy of vision correction, quality of resulting vision and reproducibility among differing patients and surgeons.