A New Technique for Precise, Predictable SBK Surgery Using the B&L Zyoptix XP Microkeratome David R. Shapiro, MD Shapiro Laser Eye Center Ventura, California No financial interest

Purpose Discuss the rationale, technique, and personal results on Sub-Bowman’s keratomileusis (SBK) performed with a 90- to 110-µm flap created with the Bausch & Lomb Zyoptix XP microkeratome

Rationale for SBK Advantages of LASIK with traditional LASIK flap Quick recovery without the pain, slow recovery and possible haze associated with PRK Advantages of surface ablation procedures Avoid biomechanical weakening of the cornea and possible dry eye following standard LASIK flaps Reduces possibility of ectasia compared with LASIK SBK may combine the best advantages of LASIK and surface ablation

SBK Flap SBK flap defined by 3 characteristics (as described by Slade and Durrie) 1 Thickness 90 to 110-µm Planar Customized diameter  Minimized to coincide with the edge of the laser ablation 1 Slade SG, Durrie DS. Six-month visual results of a contralateral prospective study: Surface ablation versus sub Bowman’s keratomileusis flaps. Presented at ASCRS Annual Meeting; San Diego; April 2007.

Ideal Flap: Thickness SBK with a flap of approximately 100-µm may combine the best features of PRK and LASIK 1,2 Biomechanical stability Quick recovery Lack of haze 1 Marshall J, Angunawela R, Tengroth J, et al. Wound healing and biomechanics of corneal flap creation. Keynote address. XXIV Congress of the ESCRS, London; Marshall J. Sub-Bowman’s keratomileusis (SBK) vs. PRK. Presented at 11th ESCRS Winter Refractive Meeting; Athens, 2007.

Both flaps exhibit planar flap architecture (uniform thickness center through the periphery) Images taken with Visante anterior segment, high resolution, non-contact optical coherence tomography (Carl Zeiss, Medictec, Inc.) Images courtesy of Barbara Lege, M.D. Munich, Germany. Ideal Flap: Planar Flap made with Zyoptix XP microkeratome Flap made with the Intralase FS30

Ideal Flap: Diameter Customized flap diameter, the third characteristic of SBK (as defined by Slade and Durrie), may not be significant Flap approximately 100 µm thick has no significant biomechanical weakening effect due to the strength of the underlying corneal tissue 1,2 Due to crossing angle differences, peripheral collagen is stronger than central collagen, theoretically further diminishing any trivial effect of increasing flap diameter 1,2 1 Marshall J, Angunawela R, Tengroth J,et al. Wound healing and biomechanics of corneal flap creation. Keynote address. XXIV Congress of the ESCRS, London; Marshall J. Sub-Bowman’s keratomileusis (SBK) vs. PRK. Presented at 11th ESCRS Winter Refractive Meeting; Athens, 2007.

Sub-Bowman’s Keratomileusis with the Zyoptix XP Microkeratome Study Methods First eye of patient: 9.5 mm diameter,19 - mm suction ring, 120-µm microkeratome head Second eye of patient: 9.5 mm diameter, 20 -mm suction ring, 120-µm microkeratome head Surgical technique in all eyes: Neutral to the z-axis (results in suction inherent to that from the machine) Subtraction pachymetry for flap measurements

SBK Results First eye (N=20) 19 mm ring 9.5 mm diameter Second eye (N=12) 20 mm ring 9.5 mm diameter Preop Corneal Thickness (µm) Mean ± SD Min, Max ± , ± , 578 Postop Corneal Thickness (µm) Mean ± SD Min, Max ± , ± , 493 Diff. Pre to Post Min, Max ± , ± , 107

Zyoptix SBK Flap Results Zyoptix XP microkeratome with this new technique safely and reproducibly produced an SBK flap Buttonholes or free caps were not seen The XP flap can be tailored for each individual eye in diameter, hinge position, and centration on the cornea The Zyoptix XP shows less variation in flap thickness than the Hansatome and is less affected by measurable preoperative variables, such as spherical equivalent

Limitations of Study Small Cohort Use of subtraction pachymetry Future Study Large cohort Flap measurement with Optical Coherence Tomography

Our study suggests that the surgeon can enjoy performing SBK effectively and safely without the need to procure an entirely different set of flap making equipment Conclusion