EyeWorld Asia-Pacific June 2011 Issue

21 EW REFRACTIVE June 2011 with hinge angle of 50°, and side- cut energy of 1.05 µJ with side-cut angle of 70°. Pocket was enabled in both eyes at 240 µm. Flap creation was performed uneventfully; John CHANG, MD Director, Guy Hugh Chan Refractive Surgery Centre, Hong Kong Sanatorium and Hospital 8/F Li Shu Pui Block, Phase II, 2 Village Road, Happy Valley, Hong Kong Tel. no. +852-2835-8885 Fax no. +852-2835-8887 johnchang@hksh.com T he femtosecond laser is now the preferred procedure for both patients and surgeons because it affords high predictability and safety. In our recent paper of 3,009 patients, we reported a complication rate of 0.63%.1 The complications that occur with the femtosecond procedure tend to be much milder and less sight-threatening to the patient’s vision. With microkeratomes, buttonhole, uneven bed and free flap can cause significant visual loss. In addition, the accuracy of the femtosecond laser cut has been found to be approximately ±10 microns in almost all machines.2-6 The case described by Dr. Kymiomis can occur if the cone (patient interface) is thick. However, while dissecting the flap, it is possible that the loose epithelium was dissected away from the Bowman’s and mistaken as a flap. Although we have not performed studies, our impression is that Chinese men tend to have looser epithelium than women, especially over 40 years old. A review by Das and Seitz7 reported a conflicting result of whether recurrent corneal erosion is more predominant in male or female while a retrospective study by Reeves et al.8 found that more women suffered from the problem. When one suspects that the epithelium is dissected away from the Bowman’s, one should return to the side cut, probe deeper along the vertical dissection (side cut) to see if there is a deeper lamellar cut that can be separated. It is unclear if Dr. Kymionis did this in his case.9 If it was indeed an epithelium-only cut, the bubbles should behave differently; they tend to form large bubbles immediately and prevent further dissection. We routinely keep our cones and when problems occur, the cone thickness can be measured. When there is indeed an epithelium-only flap, then Dr. Kymionis is correct with proceeding with PRK and the use of Mitomycin C. For higher myopes (e.g., over –6 D) and provided the patient has enough corneal thickness, I would prefer to defer the surgery to another day, cut 40 microns deeper with the IntraLase, or, failing that, use a microkeratome. References 1. Chang JS. Complications of sub-Bowman’s keratomileusis with a femtosecond laser in 3009 eyes. J Refract Surg. 2008;24(1):S97-101. 2. Issa A, Al Hassany U. Femtosecond laser flap parameters and visual outcomes in laser in situ keratomileusis. J Cataract Refract Surg. 2011;37(4):665-74. 3. Rosa AM, Neto Murta J, Quadrado MJ, et al. Femtosecond laser versus mechanical microkeratomes for flap creation in laser in situ keratomileusis and effect of postoperative measurement interval on estimated femtosecond flap thickness. J Cataract Refract Surg. 2009;35(5):833-8. 4. Reinstein DZ, Archer TJ, Gobbe M, et al. Accuracy and reproducibility of artemis central flap thickness and visual outcomes of LASIK with the Carl Zeiss Meditec VisuMax femtosecond laser and MEL 80 excimer laser platforms. J Refract Surg. 2010;26(2):107-19. Epub 2010 Feb 12. 5. Sutton G, Hodge C. Accuracy and precision of LASIK flap thickness using the IntraLase femtosecond laser in 1000 consecutive cases. J Refract Surg. 2008;24(8):802-6. 6. Vryghem JC, Devogelaere T, Stodulka P. Efficacy, safety, and flap dimensions of a new femtosecond laser for laser in situ keratomileusis. J Cataract Refract Surg . 2010;36(3):442-8. 7. Das S, Seitz B. Recurrent corneal erosion syndrome. Surv Ophthalmol. 2008 Jan-Feb;53(1):3-15. 8. Reeves SW, Kang PC, Zlogar DF, et al. Recurrent Corneal Erosion Syndrome: A Study of 364 Episodes. Ophthalmic Surg Lasers Imaging. 2010 Mar 9:1-2. doi: 10.3928/15428877-20100215-44. [Epub ahead of print] 9. Kymionis GD, Portaliou DM, Krasia MS, et al. Unintended epithelium-only flap creation using a femtosecond laser during LASIK. J Refract Surg. 2011;27(1):74-6. Epub 2010 Jun 1. Editors’ note: In the last year, Dr. Chang received lecture honorariums from Abbott Medical Optics and Technolas Perfect Vision (Munich, Germany). however, the created flaps were much thinner than expected in both eyes.” The flaps were torn with ease during lifting, and the procedure was turned into a PRK. Mitomycin C (MMC) and a bandage contact lens facilitated that procedure. After a course of antibiotics, steroid drops and artificial tears, the patient achieved 20/25 (6/7.5) in the right eye and 20/20 in the left eye with no corneal haze at 3 months post-op. Dr. Kymionis hypothesized that epithelial flap creation may have occurred as a result of inadequate corneal applanation related to the glass cone, although he could not confirm this. “A similar case of thin flap creation including stroma suggests … that femtosecond laser flap thickness creation is correlated to cone glass thickness, and thicker glass cones may produce thinner than usual flaps,” Dr. Kymionis reported. “In our case, we did not measure glass cone thickness and therefore we cannot confirm or exclude this possibility.” Dr. Kymionis added that an epithelium-only flap can be managed by conversion to PRK but advised using MMC when doing so. “The use of MMC was necessary to avoid severe postoperative haze formation due to the high attempted myopic correction,” Dr. Kymionis reported. Francis S. Mah, MD, co-medical director, Charles T. Campbell Ophthalmic Microbiology Laboratory, University of Pittsburgh School of Medicine, Pittsburgh, Pa., USA, wasn’t surprised that femtosecond lasers could have such hiccups from time to time. “There isn’t anything that is 100% foolproof,” Dr. Mah said. In order to avoid femtosecond problems, Dr. Mah said it’s important to first advise patients of these issues. Further, be vigilant, he said. “Make sure you’re not going through the same motions you’ve gone through a thousand times before,” Dr. Mah said. “Be meticulous.” LASIK is highly effective and safe, Dr. Mah said. Just consistently be alert, he reiterated. EW Editors’ note: Dr. Kymionis reported no financial interests related to this study. Dr. Mah has no financial interests related to his comments. Contact information Kymionis: kymionis@med.uoc.gr Mah: 412-647-2211, mahfs@upmc.edu