Femtosecond Laser ‘Second Pass’ for Incomplete LASIK Flaps Due to Suction Loss and Analysis of Flap Morphology 1 Anil Vedula*, Takeshi Ide*, Payman Haft* Mohamed F. Abou Shousha*, Sonia H. Yoo** *No Financial Interest **Consultant for AMO/Intralase

2 Purpose Femtosecond Laser assisted flap creation for LASIK has been introduced for LASIK surgery flap creation in recent years. Herein we examine the efficacy of performing a second pass for incomplete flap completion, focusing on the IntraLase® Femtosecond System.Femtosecond Laser assisted flap creation for LASIK has been introduced for LASIK surgery flap creation in recent years. Herein we examine the efficacy of performing a second pass for incomplete flap completion, focusing on the IntraLase® Femtosecond System.

3 Methods Twenty porcine eyes were assigned to four groups.Twenty porcine eyes were assigned to four groups. Effect of the Opaque Bubble Layer:Effect of the Opaque Bubble Layer: Two femtosecond (FS)* laser assisted flaps were created using a centrally black-painted applanator and a normal applanator, at depths of 200μm and 400μm respectfully. Two femtosecond (FS)* laser assisted flaps were created using a centrally black-painted applanator and a normal applanator, at depths of 200μm and 400μm respectfully. In group 1, flaps were created consecutively; whereas in group 2, the deeper flap was created after the opaque bubble layer (OBL) cleared. In group 1, flaps were created consecutively; whereas in group 2, the deeper flap was created after the opaque bubble layer (OBL) cleared. Simulated Incomplete Flap and Second Pass:Simulated Incomplete Flap and Second Pass: In groups 3 and 4, intentional suction loss was induced during a 150μm FS flap creation. A second pass to complete the flap at the same depth was performed prior to and after OBL clearance. In groups 3 and 4, intentional suction loss was induced during a 150μm FS flap creation. A second pass to complete the flap at the same depth was performed prior to and after OBL clearance. Gross flap characteristics were analyzed microscopically and with anterior segment OCT.Gross flap characteristics were analyzed microscopically and with anterior segment OCT. *IntraLase® Femtosecond System; Advanced Medical Optics, Inc., Santa Ana, CA.*IntraLase® Femtosecond System; Advanced Medical Optics, Inc., Santa Ana, CA. Settings: Settings: 30 KHz laser, raster bed energy 1.9μJ, side-cut energy 2.3μJ, raster spot and line separation 11 and 9μm, respectively

4 Results In group 1, we observed the peripheral shallow and the central deep cuts on the OCT and the corresponding findings under the microscope.In group 1, we observed the peripheral shallow and the central deep cuts on the OCT and the corresponding findings under the microscope. In group 2, two parallel lines appeared on the OCT corresponding to dual flaps which coincided centrally.In group 2, two parallel lines appeared on the OCT corresponding to dual flaps which coincided centrally. In groups 3 and 4, we observed lines and irregularities on the bed and the base of the flap irrespective of resolution of the OBL.In groups 3 and 4, we observed lines and irregularities on the bed and the base of the flap irrespective of resolution of the OBL.

5 Figure 1: The Effect of the Opaque Bubble Layer (OBL). A 200μm Intralase® flap was initially made with an applanation cone marked centrally to block laser tissue penetration in the center (A,B,E,F). A 400μm flap was then constructed with a normal cone before (C,D) and after the OBL cleared (G,H).

6 Figure 2: Flap Lifting and Separation after IntraLase®: Group 1: easy flap lift peripherally (A), difficult lift centrally (B). Concave shape in the central area after lift corresponding to the OCT image (C,D). Group 2: flap lift (E,F) and splitting into 2 flaps (G),and difficult separation of central area (H).

7 Figure3: IntraLase® and OCT images. The first 200μm IntraLase® cut performed peripherally with the patterned applanator (A, upper line) and the second 400μm cut with the usual cone (A, lower line). Group 1: (OBL present group) (B,C) with a deep central cut and shallow peripheral cut. Group 2:(OBL cleared group) (D,E) with two parallel lines observed.

8 Figure 4: Simulation of IntraLase® Double Pass With a Primary Incomplete and Secondary Complete 150μm IntraLase® flap made before (A,B) or after (E,F) the OBL has cleared. In both groups, two focal lines of gross flap irregularities were observed in the posterior flap (C,G) and stromal bed (D,H), which likely correlate with difficulties seen during flap lifting. These irregularities were present due to the inability to immediately stop the FS laser during suction loss occurrence (black and white arrow).

9 Conclusions A second femtosecond laser for incomplete flaps, despite clearance of OBL, may result in an uneven lamellar cut including:A second femtosecond laser for incomplete flaps, despite clearance of OBL, may result in an uneven lamellar cut including: irregular surfaces multiple flaps a free sliver of corneal stroma crossing of the two cut planes This may be due to differences in applanation pressure, hydration conditions and chemosis and can result in long lasting sight-threatening complications including: Mismatch of the flap and the bed Larger aberrations Glare Haloes We recommend not performing a second femtosecond laser pass for incomplete flaps, especially when the OBL has already cleared and when this occurs in the central or inferior cornea, an area that is critical for visual quality.

10 Limitations Porcine eyes were used for experimentation. Suction was performed on the cornea and not on the conjunctiva secondary to large porcine corneal diameters. A 150µm-depth setting was used for Group 3 and 4 which is not the usual depth with LASIK flap creation in human eyes. There are four different commercially available femtosecond lasers on the market and our experimental second pass results may be relevant only for femtosecond lasers which need a flattened cornea for creating a LASIK flap. IntraLase® IntraLase® and FEMTO LDV TM (Ziemer Ophthalmic Systems, Port, Switzerland) work with the same principle in which a flat applanator makes the cornea flat during flap creation. VisuMax (Carl Zeiss Meditec AG, Jena, Germany) and FEMTEC (20/10 Perfect Vision, Heidelberg, Germany) employ spherical applanation and low suction pressure.

11 Future Studies Further studies and case series.Further studies and case series. Using other femtosecond laser technologies to decipher further problems and solutions.Using other femtosecond laser technologies to decipher further problems and solutions. Higher quality anterior segment imaging to aid in our understanding.Higher quality anterior segment imaging to aid in our understanding.