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FIFTH GENERATION FEMTOSECOND LASER FLAP THICKNESS
Mohamed A Guenena, MDHelga P Sandoval, MD, MSCR, Kerry D Solomon, MD
Magill research center for vision correctionStorm Eye Institute
Medical University of South CarolinaFINANCIAL DISCLOSURE: None of the authors has any financial interest in any product mentioned hereinMohamed A. Guenena: NoneHelga P. Sandoval: Alcon Laboratories, Inc. - D; Allergan, Inc. - D; Abbott Medical Optics - DKerry D. Solomon: Alcon Laboratories, Inc. - A,C,D; Allergan, Inc. - A,C,D; Abbott Medical Optics - A,C,D; Advanced Vision Research - A,C,D; Bausch & Lomb, Inc. - A,C,D; Eyemaginations - A,C,D; QLT, Inc. - A,C,D
PURPOSE
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
METHODS
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
OCT SETTINGS:
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
A B C D
Line 1
Line 2 Line 3Line 4
Pre and Postoperative Data
Intraoperative Pachymetry was done by subtraction method
ASCRS 2009
Pre-operative Post-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
-2.73 (-7.75― 2.25) 0 (-0.37―0.25)
Pachymetry 565 ( 535―596) NA
100 µm flaps 110 µm flaps
Number of eyes 4 18
Flap thickness by US pachymetry
109 µm (±9.6) 119 µm (±11.5)
RESULTS
ASCRS 2009
OCT picture showing the four points measurements for a single line scan in a patient who had a 110 µm flap
OCT RESULTS
Attempted Flap thickness
Number of eyes
OCT measurementsMean
Std Dev
100 µm 2 117 µm 11.2
110 µm 4 123 µm 6.5
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 A Point B Point C Point D
Average thickness
119 µm (±10.9)
124 µm (±4.4)
124 µm (±7.5)
124 µm (±6.4)
OCT RESULTS
Comparing the flap thickness by lines for the 110µm group
ASCRS 2009
Line 1 Line 2 Line 3 Line 4
Average thickness
121 µm (±7.1)
124 µm(±5.5)
124 µm(±7.4)
124 µm(±6)
CONCLUSION
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