Mohamed A Guenena, MD Helga P Sandoval, MD, MSCR, Kerry D Solomon, MD Magill research center for vision correction Storm Eye Institute Medical University of South Carolina

 To assess the accuracy and reproducibility of flap thickness created by the fifth generation femtosecond laser using:  Intraoperative pachymetry  Postoperative anterior segment OCT ASCRS 2009

 Prospective, unmasked study  24 eyes of 12 patients  Had primary LASIK surgery  Flaps created with the new 5th generation femtosecond Laser (iFS Advanced Femtosecond Laser, Abbot Medical Optics )  Attempted Flap depth  100 microns in 4 eyes  110 microns in 20 eyes  Assessment:  Intraoperative pachymetry  Postoperative anterior segment Fourier-domain optic coherence tomography (OCT) on a subgroup of patients at an average of 3 month  The SAS system software was used to analyze the results ASCRS 2009

 2 cross scans were used to measure each flap (Figure 1)  The cross scan setting entails 2x1024 A scans (8 scans in each directions are then averaged)  The LASIK flap was identified by increased reflectivity at the flap-stromal interface. then the cursor was moved manually to the interface and measurements were recorded.  On each line of the cross scan, the thickness was calculated at four points ( Figure 2)  A 2.5 mm left to the midline  B 1 mm left to midline  C 1 mm right to midline  D 2.5 mm right to midline Fig. 1 Fig. 2 ASCRS 2009 ABCD Line 1 Line 2 Line 3 Line 4

 Pre and Postoperative Data  Intraoperative Pachymetry was done by subtraction method ASCRS 2009 Pre-operativePost-operative day 30 Spherical error-2.5 (-6.2—2.2)0.1 (-0.2―1.2) Cylinder-0.7 ( -3.5―0.5)-0.2(-0.5―0) Spherical equivalent (-7.75― 2.25)0 (-0.37―0.25) Pachymetry 565 ( 535―596) NA 100 µm flaps110 µm flaps Number of eyes418 Flap thickness by US pachymetry 109 µm (±9.6)119 µm (±11.5)

ASCRS 2009 OCT picture showing the four points measurements for a single line scan in a patient who had a 110 µm flap

Attempted Flap thickness Number of eyes OCT measurements Mean Std Dev 100 µm2117 µm µm4123 µm6.5 ASCRS 2009  Overall flap thickness per group  Comparing the consistency of the flap thickness at different points in the 110 µm group in all line scans Point APoint BPoint CPoint D Average thickness 119 µm (±10.9) 124 µm (±4.4) 124 µm (±7.5) 124 µm (±6.4)

 Comparing the flap thickness by lines for the 110µm group ASCRS 2009 Line 1Line 2Line 3Line 4 Average thickness 121 µm (±7.1) 124 µm (±5.5) 124 µm (±7.4) 124 µm (±6)

 The new fifth generation femtosecond laser shows  High consistency of flap thickness  High reproducibility of flap thickness  Accurate flap thickness predictability  The flaps are uniform at different points ASCRS 2009