Authors have no financial interest E-mail: oscarmac1@hotmail.com Wavefront Aberrations Induced by Flap Creation with a Femtosecond Laser and a Mechanical Microkeratome Instituto de Oftalmología, Fundación Conde de Valenciana, I.A.P. Authors: Oscar Macías Manuel, MD Alejandro Navas Perez, MD Coauthors: Enrique Graue, MD Tito Ramírez Luquín, MD Authors have no financial interest E-mail: oscarmac1@hotmail.com

Methods In this prospective study of 9 consecutive patients, the right eye was randomized to flap creation with the Ziemer LDV, femtosecond laser (110 microns) (group 1) or Moria 2, mechanical microkeratome (90 microns) (group 2) . The left eye was assigned to the other. Corneal optical aberrations were assessed with the Nidek, OPD scan II just before, and 30 minutes after flap creation (before laser ablation). Main outcome measures: corneal wavefront aberrations before and after flap creation Statistical analysis : Comparison between eyes was examined with t test,  of 0.05. Variance was anlyzed with f test,  of 0.05

Results Before flap creation there was no difference in corneal wavefront aberrations between eyes of each patient. LDV femtosecond laser flaps (110 m): statistically significant change before and after flap creation in higher order aberrations (p = 0.034), and trefoil (p = 0.024) Moria mechanical microkeratome: significant for higher 2 order aberrations (p = 0.01), trefoil (p = 0.03), and tilt (p = 0.019) When comparing treatments there was no statistical difference (p = > 0.05). However, those eyes treated with the mechanical microkeratome had an increased variance for tilt (p = < 0.001), coma (p = 0.02), and spherical aberration (p = <0.001)

Comparison of corneal wavefront aberrations before flap creation between femtosecond and mechanical microkeratome groups Before flap creation there was no difference in corneal optical aberrations between eyes of each patient

Comparison of corneal wavefront aberrations after flap creation between femtosecond and mechanical microkeratome treated eyes When comparing treatments there was no statistical difference (p = > 0.05)

Comparison of corneal wavefront aberrations before and after flap creation, mechanical microkeratome group Marca en colores distitnos las que son significativas In those eyes treated with the mechanical microkeratome, There was a statistical significant change for higher order aberrations (p = 0.01), and trefoil (p = 0.03)

Comparison of corneal wavefront aberrations before and after flap creation, femtosecond laser group Colores distintos para las significativas In eyes treated with the femtosecond laser, there was a statistical significant change before and after flap creation in higher order aberrations (p = 0.034), and trefoil (p = 0.024)

Variance analysis of corneal wavefront aberrations created with the two methods Te corregi las p… creo que no vale la pena.. Con que pongas que es menor a 0.0001… Faltan las p de treofoil y tetra foil del laser, igual. Te hacen falta las barras de error.. Hay un boton que dice error Error bars y que pones las desvianciones estandar.. Variance analysis shows greater variability in wavefront corneal aberrations with those flaps created with the mechanical microkeratome (statistical significance for spherical aberration: p <0.001, astigmatic aberration: p = 0.003, and tilt: p < 0.001). Trefoil (p = 0.02) and tetrafoil (p = 0.006) aberrations showed increased variance with Femtosecond laser flap creation

Discussion Flaps created with the Femtosecond laser were intended to be 110 microns thick, while those created with the mechanical microkeratome 90 microns thick. The increased variance in the induction of higher order aberrations in the mechanical microkeratome group could be explained because of the lenticular form of the flaps created with all mechanical microkeratomes produced with the indentation of the cornea as the applanation precedes the cut of the microkeratome, producing flaps thicker in the periphery and thinner in the center. Several previous studies demonstrate that the flaps created with the femtosecond laser are more plannar, following the anterior surface of the cornea (1 – 4) . One drawback to our study is that the flap thickness is not the same between groups (diference of 20 microns), and this factor alone could provide less stability in flap creation with the mechanical microkeratome, as the cutting blade runs more superficially, thus producing increased variance in higher order aberration creation Yo basaria la discusion en que el flap de LDV es de caras paralelas y que por ello induce aberraciones mas consistentes, mientras que el menisco que forma el flap del micro k.. Pudiera ser responsible de las aberraciones mas impredecible. YO creo que hay que discutir que una de las limitatnes de este estudio es que el grosor de los dos grupos es distinto y que flaps mas guresos pueden en teroia ser mas consistentes que los flaps delgados en sus aberraciones.. Echale algo de rollo ponel la biblio y finito

Conclusions There was no difference in the induction of corneal higher order aberrations between flaps created with the femtosecond laser or with the mechanical microkeratome Variance analysis revealed that flap creation with the femtosecond laser may induce more predictable wavefront changes in spherical, tilt, and astigmatic aberrations, which may possibly increase the success of customized or optimized ablation. It has been demonstrated in other studies that fourth order aberrations, such as spherical aberration, are the ones with the most important visual impact (5 – 10)

Bibliography 1.- Lim T, Yang S, Kim M, et al. Comparison of the IntraLase femtosecond laser and mechanical microkeratome for laser in situ keratomileusis. Am J Ophthalmol 2006; 14(5):833-839 2.- Durrie DS, Kezirian GM. Femtosecond laser versus mechanical keratome flaps in wavefront guided laser in situ keratomileusis: prospective contralateral eye study. J Cataract Refract Surg 2005; 31(1): 120-126 3.- Tran DB, Sarayba MA, Bor Z, et al. Randomized prospective clinical study comparing induced aberrations with IntraLase and Hansatome flap creation in fellow eyes: potential impact on wavefront guided laser in situ keratomileusis. J Cataract Refract Surg 2005; 31(1): 97-105 4.- Aslanides IM, Tsiklis NS, Astyrakakis NI, Pallikaris IG, Jankov MR. LASIK flap characteristics using the Moria M2 microkeratome with the 90-micron single use head. J Refract Surg. 2007;23:45-49. 5.- Liang J, Williams DR. Aberrations and retinal image quality of the normal human eye. J Opt Soc Am A1997; 14: 2873-2883 6.- Yoon GY, Williams DR. Visual performance after correcting the monochromatic and chromatic aberrations of the eye. J Opt Soc Am A 2002; 19: 266-275 7.- Roorda A. A review of basic wavefront optics. In: Krueger RR, Applegate RA, MacRae SM, eds. Wavefront customized visual corrections: the quest for super vision II. Thorofare, NJ, Slack, 2004: 9-18 8.- Applegate RA, Marsack JD, Ramos R, et al. Interaction between aberrations to improve or reduce visual performance. J Cataract Refract Surg 2003; 29: 1487-1495 9.- Aplegate RA, Ballentine C, Gross H, et al. Are all aberrations equal? J Refract Surg 2002; 18: S556-S562 10.- Netto MV, Dupps W Jr, Wilson SE. Wavefront guided ablation: Evidence for efficacy compared to traditional ablation. Am J Ophthalmol 2006: 141(2): 360-368