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

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 FS۲۰۰, 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, ۱۶۸ eyes underwent flap creation using the WaveLight FS۲۰۰ laser, and on ۱۸۹ eyes, the VisuMax laser was used. Of these total number, flap morphology was analyzed in a random sample of ۱۵۸ eyes; ۸۰ with the Visumax laser and ۷۸ with the WaveLight FS۲۰۰ laser. Intraoperative photos of the flaps taken by the Wavelight Allegretto EX۵۰۰ 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 ۹۰% of patients in both groups achieved a UDVA of ۲۰/۲۰ postoperatively. The mean difference between targeted and achieved flap diameter was ۰.۵۰ +/- ۰.۱۵ mm in the VisuMax group and ۰.۳۵ +/- ۰.۱۵ millimeters (mm) in the FS۲۰۰ group (P<۰.۰۱). The flap diameters of the VisuMax group were more precise with a variance of ۰.۰۲۴ mm compared to a variance of ۰.۰۳۸ mm in the FS۲۰۰ group (P<۰.۰۵). VisuMax flaps were more nasally displaced (log(NA/TA) = -۰.۲۱ +/- ۰.۱۰ mm) compared to the FS۲۰۰ flaps (log(NA/TA) = ۰.۰۳ +/- ۰.۱۰ mm), (P< ۰.۰۱). We concluded that both the VisuMax and FS۲۰۰ 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 FS۲۰۰. 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.