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. 2019 Fall;8(3):241-249.

Comparative Analysis of LASIK Flap Diameter and its Centration Using Two Different Femtosecond Lasers

Majid Moshirfar  1   2   3 , Tanner W Brown  4   5 , Madeline B Heiland  6 , David B Rosen  6 , Yasmyne C Ronquillo  2 , Phillip C Hoopes  2
Affiliations

Comparative Analysis of LASIK Flap Diameter and its Centration Using Two Different Femtosecond Lasers

Majid Moshirfar et al. Med Hypothesis Discov Innov Ophthalmol. 2019 Fall.

Abstract

The aim of this study was to compare the diameter, accuracy, variability, and centration with respect to the limbus of corneal flaps created by two femtosecond lasers, the VisuMax, and Wavelight FS200, for laser in situ keratomileusis (LASIK) and how these flaps affect visual outcomes. This is a retrospective chart review of flap morphology created during LASIK Surgery. Overall, 168 eyes underwent flap creation using the WaveLight FS200 laser, and on 189 eyes, the VisuMax laser was used. Of these total number, flap morphology was analyzed in a random sample of 158 eyes; 80 with the Visumax laser and 78 with the WaveLight FS200 laser. Intraoperative photos of the flaps taken by the Wavelight Allegretto EX500 were analyzed. Flap diameters and centration were measured using Adobe Acrobat Pro. All patients had visual acuity measurements including uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), spherical equivalent refraction (SE) and refractive astigmatism recorded three months postoperatively. Greater than 90% of patients in both groups achieved a UDVA of 20/20 postoperatively. The mean difference between targeted and achieved flap diameter was 0.50 +/- 0.15 mm in the VisuMax group and 0.35 +/- 0.15 millimeters (mm) in the FS200 group (P<0.01). The flap diameters of the VisuMax group were more precise with a variance of 0.024 mm compared to a variance of 0.038 mm in the FS200 group (P<0.05). VisuMax flaps were more nasally displaced (log(NA/TA) = -0.21 +/- 0.10 mm) compared to the FS200 flaps (log(NA/TA) = 0.03 +/- 0.10 mm), (P< 0.01). We concluded that both the VisuMax and FS200 created flaps larger than the preoperative targeted diameter. VisuMax created corneal flaps that had a greater degree of deviation from the targeted diameter when compared to flaps from the FS200. However, there was less variance in the VisuMax flap diameter. In addition, VisuMax flaps were more nasally displaced. There were no statistically significant differences in visual outcomes when comparing the two femtosecond lasers.

Keywords: Corneal Flap; Femtosecond Laser; Flap Centration; Flap Diameter; Flap Morphology; Flap Predictability; Flap Variance; Laser; Laser In Situ Keratomileusis; VisuMax Laser.

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Conflict of interest statement

Ethical issues have been completely observed by the authors. All named authors meet the International Committee of Medical Journal Editors (ICMJE) criteria for authorship of this manuscript, take responsibility for the integrity of the work as a whole, and have given final approval for the version to be published. No conflict of interest has been presented.

Figures

Figure 1
Figure 1
Measurements: White-to-White Distance (WWM), Flap Diameter (FM), Distance from Limbus to the Flap Margin on Nasal (NM) and Temporal (TM) Sides. Abbreviation: mm: millimeters
Figure 2
Figure 2
Example of Scaled Adobe Measurements of a Nasally Displaced Flap a Nasally Displaced Flap Created by the VisuMax (log(NM/TM) = log(1.15/2.54) <0. Abbreviation: mm: millimeters
Figure 3A
Figure 3A
Nine standard graphs reporting refractive surgery outcomes of 168 eyes treated by the WaveLight FS200 laser. Visual outcomes (uncorrected distance visual acuity= UDVA, UDVA versus corrected distance visual acuity= CDVA, Change in CDVA), spherical equivalent refraction (SER), SER Attempted versus Achieved, SER accuracy, SER stability, refractive astigmatism, and surgically induced astigmatism (SIA) are depicted
Figure 3B
Figure 3B
Nine standard graphs for reporting refractive surgery outomes of 189 eyes treated by the VisuMax laser. Visual outcomes (uncorrected distance visual acuity= UDVA, UDVA versus corrected distance visual acuity= CDVA, Change in CDVA), spherical equivalent refraction (SER), SER Attempted versus Achieved, SER accuracy, SER stability, refractive astigmatism, and surgically induced astigmatism (SIA) are depicted
Figure 4
Figure 4
Comparison of targeted flap diameter and achieved flap diameter for the WaveLight FS200 and VisuMax
Figure 5
Figure 5
Analysis of variance in targeted flap diameter and achieved flap diameter for the WaveLight FS200 and VisuMax
Figure 6
Figure 6
Depiction of flap centration (nasal or temporal displacement) for the WaveLight FS200 and VisuMax in respect to the limbus
Figure 7
Figure 7
Severity of flap displacement from the limbus for the WaveLight FS200 and VisMax. grade 0: log (N A / T A ) from -0.04 to 0.04, grade 1: log(N A / T A ) from -0.18 to 0.18, grade 2: log(N A / T A ) from -0.30 to 0.30, grade 3: log(N A / T A ) from -0.40 to 0.40
Figure 8
Figure 8
Variability of flap displacement in left (OS) and right eyes (OD) for WaveLight FS200 and VisuMax
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