Dr. Emil Chynn has publish numerous articles about Advanced surface ablation technique being safer than LASIK for enhancement surgery as well as primary surgery, here is one such article.
Wilson and Santhiago report on “flaporhexis” which they describe as a new technique to lift the LASIK flap during enhancement surgery.1 Their stated advantage of using this technique is that it “produces a smooth epithelial dissection and deceases the possibility that epithelium is retained beneath the flap.”Last year, Guell, et. al. reported their new technique for performing LASIK enhancements using the femtosecond laser to create a vertical side-cut incision.2 Again, their stated advantage of performing an additional incision—using an additional laser—was to decrease the chance of epithelial ingrowth after manual dissection of a primary flap, the incidence of which has been reported in the literature to range from 2% to 43%.3-5
Wilson does not mention the alternative of photorefractive keratectomy (PRK) over a previous LASIK flap. Guell does suggest that the primary indications for PRK over LASIK is “in cases of thin residual stromal thickness and flap irregularities (i.e., microfolds).”
It is thus widely agreed that the most common and problematic complication encountered when enhancing prior LASIK surgery by the “lift and re-laser” technique is epithelial ingrowth. However, there is no way to eliminate this complication if manually dissecting the existing LASIK flap, even if employing this “rhexis” technique. Similarly, although the femtosecond vertical side-cut may produce a tighter fitting “manhole” cover, an additional vertical track is still being created, through which epithelial cells can migrate. Indeed, Guell reports the novel complication of “loss of a sliver of tissue between the old angular side cut and the new vertical side cut.” Presumably, the incidence of epithelial ingrowth in such cases would be increased.
For the past five years, I have enhanced prior LASIK surgeries exclusively by performing LASEK (alcohol-assisted epithelial removal + surface ablation). Besides decreasing the risk of epithelial ingrowth to zero, this technique has another, more important advantage—not decreasing residual stromal bed (RSB) and thus not increasing the risk of iatrogenic ectasia.
In complicated enhancements patients often report subjective visual complaints that may be worse than their Snellen acuity, due to higher order aberrations (HOA). When we changed our enhancement technique from “lift and relaser” to “LASEK over LASIK” our patients had greater improvement in their subjective visual complaints. We hypothesize this is because the wavefront map that we obtain and ablate is exactly what is required, and not distorted by re-lifting the flap.
It is important to stress that the use of mitomycin-c (MMC) is essential to prevent scarring when performing Advanced Surface Ablation (ASA) enhancements of prior LASIKs. We look forward to controlled studies to determine which enhancement technique has the best risk-reward ratio (especially with regard to epithelial ingrowth & ectasia), so should eventually predominate.
Emil William Chynn, MD, MBA dr@ParkAvenueLASEK.com
Jyoti Puri, MD
Patricia Villaroel, MD
Elias Almeida, MD
Nishit Shah, MD
New York, NY
1Wilson SE, Santhiago MR. Flaporhexis: rapid and effective technique to limit epithelial ingrowth after LASIK enhancement. J Cataract Refract Surg 2012; 38:2−4
2Guell JL, Elies D, Gris O, Manero F, Morral M. Femtosecond laser-assisted enhancements after laser in situ keratomileusis. J Cataract Refrac Surg 2001; 37:1928−1931
3Chan CCK, Boxer Wachler BS. Comparison of the effects of LASIK retreatment techniques on epithelial ingrowth cases. Ophthalmology 2007; 114:640−642
4Caster AI, Friess DW, Schwendeman FJ. Incidence of epithelial ingrowth in primary and retreatment of laser in situ keratomileusis. J Cataract Refract Surg 2010; 36:97−101
5Letko E, Price MO, Price FW Jr. Influence of original flap creation method on incidence of epithelial ingrowth after LASIK retreatment. J Refract Surg 2009; 25:103901041